Dynamic fixation assemblies with inner core and outer coil-like member

ABSTRACT

A dynamic fixation medical implant includes a longitudinal connecting member assembly having an elongate coil-like outer member and an inner cylindrical core attached to the outer member at only one end thereof. Some assemblies include a second longitudinal connecting member in the form of a rod that is fixed to the inner core and extends outwardly from the assembly. Certain assemblies include a threaded core or threaded inserts that cooperate with a helical slit of the coil-like outer member. Two or more cooperating bone screw assemblies attach to the connecting member assembly. The bone screw assemblies may include upper and lower compression members for affixing to and cradling the coil-like outer member only, allowing relative movement between the outer member and the inner cylindrical core. Press fit or snap-on features attach one end of the coil-like outer member to one end of the inner cylindrical core.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the following U.S. ProvisionalApplications: No. 60/722,300 filed Sep. 30, 2005; No. 60/725,445 filedOct. 11, 2005; No. 60/728,912 filed Oct. 21, 2005; No. 60/736,112 filedNov. 10, 2005; and No. 60/832,644 filed Jul. 21, 2006; all of which areincorporated by reference herein. This application is also acontinuation-in-part of the following U.S. patent applications, all ofwhich are incorporated by reference herein: Ser. No. 11/328,481 filedJan. 9, 2006 which is a continuation-in-part of Ser. No. 11/272,508filed Nov. 10, 2005 that claims the benefit of U.S. ProvisionalApplication No. 60/630,536 filed Nov. 23, 2004 and which is acontinuation-in-part of Ser. No. 10/996,289, filed Nov. 23, 2004, andwhich is a continuation-in-part of Ser. No. 10/789,149, filed Feb. 27,2004; a continuation-in-part of Ser. No. 11/178,854 filed Jul. 11, 2005which claims benefit of U.S. Provisional Application No. 60/655,239filed Feb. 22, 2005; a continuation-in-part of Ser. No. 10/986,377 filedNov. 10, 2004; and a continuation-in-part of Ser. No. 11/024,543 filedDec. 20, 2004.

BACKGROUND OF THE INVENTION

The present invention is directed to dynamic fixation assemblies for usein bone surgery, particularly spinal surgery, and in particular tolongitudinal connecting members and cooperating bone anchors orfasteners for such assemblies, the connecting members being attached toat least two bone fasteners.

Historically, it has been common to fuse adjacent vertebrae that areplaced in fixed relation by the installation therealong of bone screwsor other bone anchors and cooperating longitudinal connecting members orother elongate members. Fusion results in the permanent immobilizationof one or more of the intervertebral joints. Because the anchoring ofbone screws, hooks and other types of anchors directly to a vertebra canresult in significant forces being placed on the vertebra, and suchforces may ultimately result in the loosening of the bone screw or otheranchor from the vertebra, fusion allows for the growth and developmentof a bone counterpart to the longitudinal connecting member that canmaintain the spine in the desired position even if the implantsultimately fail or are removed. Because fusion has been a desiredcomponent of spinal stabilization procedures, longitudinal connectingmembers have been designed that are of a material, size and shape tolargely resist flexure, extension, torsion, distraction and compression,and thus substantially immobilize the portion of the spine that is to befused. Thus, longitudinal connecting members are typically uniform alongan entire length thereof, and usually made from a single or integralpiece of material having a uniform diameter or width of a size toprovide substantially rigid support in all planes.

Fusion, however, has some undesirable side effects. One apparent sideeffect is the immobilization of a portion of the spine. Furthermore,although fusion may result in a strengthened portion of the spine, italso has been linked to more rapid degeneration and even hyper-mobilityand collapse of spinal motion segments that are adjacent to the portionof the spine being fused, reducing or eliminating the ability of suchspinal joints to move in a more normal relation to one another. Incertain instances, fusion has also failed to provide pain relief.

An alternative to fusion and the use of more rigid longitudinalconnecting members or other rigid structure has been a “soft” or“dynamic” stabilization approach in which a flexible loop-, S-, C- orU-shaped member or a coil-like and/or a spring-like member is utilizedas an elastic longitudinal connecting member fixed between a pair ofpedicle screws in an attempt to create, as much as possible, a normalloading pattern between the vertebrae in flexion, extension,distraction, compression, side bending and torsion. Problems may arisewith such devices, however, including lack of adequate spinal supportand lack of fatigue strength or endurance limit. Fatigue strength hasbeen defined as the repeated loading and unloading of a specific stresson a material structure until it fails. Fatigue strength can be tensileor distraction, compression, shear, torsion, bending, or a combinationof these. The complex dynamic conditions associated with spinal movementtherefore provide quite a challenge for the design of elongate elasticlongitudinal connecting members that exhibit an adequate fatiguestrength to provide stabilization and protected motion of the spine,without fusion, and allow for some natural movement of the portion ofthe spine being reinforced and supported by the elongate elastic orflexible connecting member.

SUMMARY OF THE INVENTION

Polyaxial bone screw assemblies according to the invention includelongitudinal connecting members that provide dynamic, protected motionof the spine. One aspect of the invention is a dynamic medical implantassembly that includes at least two bone attachment structures andfurther includes an elastic and flexible longitudinal connecting memberhaving an inner cylindrical core and an outer coil-like member. In aneutral unloaded position, the outer coil-like member is in contact withand attached to the cylindrical core at only one location. Thecylindrical core is receivable in the coil-like member along asubstantial length thereof. The outer coil-like member is thus insliding engagement with the inner cylindrical core in both an axialdirection and torsionally about a substantial length of the core whenthe core is fixed with respect to coil-like member at a discretelocation, for example at ends thereof.

According to another aspect of the invention, the inner cylindrical coreincludes a helical thread for cooperating with the outer coil-likemember. The thread may be integral with or otherwise fixed to the innercylindrical core. The thread of the cylindrical core has substantiallythe same pitch as the helical slit of the outer coil-like member and isthus threadably receivable in the outer member adjacent to the internalsurface and extending along a substantial length of the outer member.The outer coil-like member is in sliding engagement with the innercylindrical core in a direction along the axis and torsionally when thecore is fixed to and/or in contact with the coil-like member at one endthereof. The inner thread is sized and shaped to extend only partiallyinto the helical slit of the outer core. Furthermore, the thread isspaced from the coil surfaces defining the helical slit, such that thereis an axial gap between the core thread and the surfaces defining thehelical slit. The threaded core and the coil may be coated, usingmethods such as ion bonding, to provide an ultra hard, ultra thin, ultrasmooth and ultra slick coating to provide wear resistant hardness andlimited wear debris between the contact surfaces.

According to another aspect of the invention, one or more threadedinserts are provided that slidingly mate with the inner cylindrical coreand threadably cooperate with the outer coil-like member. The inner corefurther includes a support structure fixedly attached or integralthereto, that may be, for example, a solid rod disposed at an end of theinner core and sized and shaped to extend outwardly away from thecoil-like member. Alternatively or additionally, the support structuremay be in the form of a helical projection disposed at any desiredlocation along the inner core and sized and shaped to protect the outercoil-like flexible member from being crushed or otherwise deformed by aclosure member or compression insert pressing against the flexiblemember at the bone attachment structure. One or more tubular adjustablesupport structures are also provided, each with a helical projection forcooperation with the outer coil-like member. The tubular supportstructures are receivable on the inner core with the thread thereofreceivable in the slit of the coil-like member and also extendibletherethrough. In one of the illustrated embodiments, the outer coil-likemember is clamped to each of the bone attachment structures at thelocation of the fixed and adjustable tubular supports, with theprojection of each respective support extending through the slit in theouter flexible member directly resisting clamping pressure exerted by aclosure structure or other compression member or insert that captures orotherwise connects with the longitudinal connecting member within areceiver of the attachment structure.

In the illustrated embodiments, the outer coil-like member includes aninternal substantially cylindrical surface and an external substantiallycylindrical surface. The outer coil-like member further defines ahelical slit extending through the internal surface and the externalsurface and also preferably runs along a substantial length of thecoil-like member and may include the entire length of the coil-likemember. The cylindrical core is thus receivable in the outer memberadjacent to the internal surface and extends along a substantial lengthof the outer member, the outer coil-like member being moveable withrespect to the inner cylindrical core in a direction along the axis andtorsionally when the core is fixed to and/or in contact with thecoil-like member at least one location. While the illustrated embodimentof the invention are illustrated as linear, it is foreseen that theycould be curvilinear.

In certain embodiments of the invention, the inner cylindrical core maybe connected to the coil-like member with a snap-on, press fit, or othertype of connection. Alternatively or additionally, when the inner coreincludes a helical thread, an end portion of the helical thread may bethickened to engage the coil-like member surfaces at the helical slitthereof, and be of a radial length to completely extend through thehelical slit of the coil-like member. This creates a type of press fitbetween the core and coil-like member that is reinforced when a boneattachment structure placed at the press fit location presses againstboth the coil and a portion of the thread of the core. The threadwinding along a remainder of the core has an outer diameter that isreduced, such that any other bone attachment structures along the lengthof the core and coil combination do not press against the thread of thecore, but press exclusively against the coil outer cylindrical surface.

According to an aspect of the invention, the outer coil-like memberexternal surface is clamped to each of the bone attachment structures insuch a manner that the inner cylindrical core remains movable withrespect to the outer coil-like member internal surface and also with atleast one bone attachment structure and therefore the cylindrical coredoes not participate in or provide any means for torsional elasticity oraxial compression and distraction along the coil-like member.Specifically, upper and lower compression members disposed in each ofthe bone attachment structures have radiused inner surfaces sized andshaped for exclusive frictional engagement with the outer coil-likemember external surface. The compression members cooperate to clamp onlythe outer coil to one or more of the bone attachment structures and notcrush or otherwise press against the inner cylindrical core on at leastone end thereof. Thus the inner cylindrical core remains in slidablerelationship with respect to the outer coil-like member along a lengththereof. In certain embodiments the upper and lower compression membersdirectly contact one another, with the upper compression member pressingupon both the lower compression member and the outer coil-like member.In another illustrated embodiment, the compression members cooperatewith a closure structure that includes an outer fastener and an innerset screw. The outer fastener is pressable upon the lower compressionmember while the inner set screw is pressable on the upper compressionmember, the upper and lower compression members being in slidablecontact.

According to another aspect of the invention, the bone attachmentstructure includes a shank or other anchor that has a surface altered bya surface roughening treatment and/or a coating to provide a bioactiveinterface between the bone attachment structure and a vertebra, or atleast some component of bone bonding or bone ingrowth into the bonescrew shank or other anchor. Such assemblies may include bone screwshanks that are either treated to provide for a roughened or poroussurface, such as by plasma spraying, cleaning or coating. Furthermore,such treatment may include coating with a metal to create a scaffold forbone ingrowth or coating with other materials such as calcium phosphatebio-ceramics including hydroxyapatite and tri-calcium phosphate thatactively take part in bone bonding. A further aspect of the inventionincludes providing the longitudinal connecting member with a coating,slit filling and/or covering or sheath sized and shaped to prevent boneand/or soft tissue ingrowth on or in the coil-like member and thehelical slit or slits formed thereby. In addition, the inner core and/orinternal surface of the coil-like member can be coated, chemicallytreated or sheathed with hard, low friction materials to improveperformance and decrease wear debris.

According to a further aspect of the invention, the smooth cylindricalor threaded inner core may be fixedly attached or integral with anadditional connecting member at one end thereof, that is illustratedherein as a rod having a length for attachment to at least one and up toa plurality of bone screws. The illustrated additional connecting memberis solid, but may be hollow, and typically has a diameter greater than adiameter of the inner core but of equal, greater or lesser diameter thanan outer diameter of the coil-like member. The additional connectingmember is typically cylindrical, having a circular cross section, butmay also be of other shapes including rectangular, square, or otherpolygonal or curved cross sections.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, it is an object of the present invention to overcome one ormore of the problems with bone attachment assemblies described above. Anobject of the invention is to provide dynamic medical implantstabilization assemblies having longitudinal connecting members thatinclude an inner core insertable into an outer coil-like portion that ismovable relative to the inner core when implanted. Another object of theinvention is to provide dynamic medical implant stabilization assembliesthat include bone screws having an affinity to bone. Also, it is anobject of the invention to provide a bone fixation assembly thatincludes a receiver with an open channel, a shank pivotally, hingedly,or otherwise connected to the receiver, a longitudinal connecting memberhaving a coil-like outer portion and an inner cylindrical core, a firstlower compression structure disposed between the shank and theconnecting member and a second upper compression structure disposedbetween the connecting member and a closure, the first and secondcompression members engaging the coil-like outer portion withoutengaging the inner cylindrical core. A further or alternative object ofthe invention is to provide adjustable inserts for such longitudinalconnecting members for placement within a bone screw receiver or otherbone attachment member, providing for adequate gripping and clamping ofthe longitudinal assembly as well as directly resisting clampingpressure, thus protecting the longitudinal member from deformation dueto clamping forces. Another object of the invention is to provide a morerigid or solid connecting member surface, if desired, such as a solidrod portion integral or otherwise fixed to the inner core for bone screwattachment to such solid surface. Additionally, it is an object of theinvention to provide a lightweight, reduced volume, low profile assemblyincluding at least two bone screws and a longitudinal connecting membertherebetween. Furthermore, it is an object of the invention to provideapparatus and methods that are easy to use and especially adapted forthe intended use thereof and wherein the apparatus are comparativelyinexpensive to make and suitable for use.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded and partial front elevational view of a dynamicfixation connecting member assembly according to the invention includinga coil-like member and a cylindrical core.

FIG. 2 is an exploded and partial cross-sectional view taken along theline 2-2 of FIG. 1.

FIG. 3 is a cross-sectional view of the coil-like member, taken alongthe line 3-3 of FIG. 1.

FIG. 4 is a cross-sectional view of the cylindrical core, taken alongthe line 4-4 of FIG. 1.

FIG. 5 is a partial and exploded perspective view of a dynamic fixationbone screw assembly according to the invention including a bone screwshank, a receiver, a retaining structure, a first lower compressionmember, the dynamic fixation connecting member assembly of FIG. 1, asecond upper compression member and a closure member.

FIG. 6 is an enlarged perspective view of an assembled dynamic fixationassembly of FIG. 5 with portions broken away to show detail thereof.

FIG. 7 is an enlarged and partial cross-sectional view taken along theline 7-7 of FIG. 6 of the receiver, the first and second compressionmembers, the dynamic fixation connecting member assembly and the closuremember, also shown with the shank in side elevation implanted in avertebra and disposed at an angle with respect to the receiver.

FIG. 8 is an enlarged and partial cross-sectional view, similar to FIG.7, shown without the closure member and showing the dynamic fixationconnecting member assembly and the second upper compression memberremoved and further showing a different sized connecting member andcooperating upper compression member for insertion in the receiver.

FIG. 9 is an enlarged and partial cross-sectional view, similar to FIGS.7 and 8, showing the different sized connecting member and cooperatingupper compression member fully inserted in the receiver with the sameclosure top as illustrated in FIG. 7.

FIG. 10 is an exploded and partial front elevational view of a secondembodiment of a dynamic fixation connecting member assembly according tothe invention including a coil-like outer member and an inner threadedcore.

FIG. 11 is an exploded and partial cross-sectional view taken along theline 11-11 of FIG. 10.

FIG. 12 is a partial front elevational view of the dynamic fixationconnecting member of FIG. 10, showing the threaded core fully insertedin the coil-like member.

FIG. 13 is an enlarged and partial cross-sectional view taken along theline 13-13 of FIG. 12.

FIG. 14 is a partial and exploded perspective view of the dynamicfixation assembly according to the invention illustrated in FIG. 5replacing the connecting member assembly of FIGS. 1-4 with theconnecting member assembly of FIGS. 10-13.

FIG. 15 is an enlarged perspective view of an assembled dynamic fixationassembly of FIG. 14 with portions broken away to show detail thereof.

FIG. 16 is an enlarged and partial cross-sectional view taken along theline 16-16 of FIG. 15 and along the line 16-16 of FIG. 12, but shownwith the shank in side elevation implanted in a vertebra and disposed atan angle with respect to the receiver.

FIG. 17 is an enlarged and partial cross-sectional view, similar to FIG.16, showing a second bone screw assembly attached to the dynamicfixation assembly of FIG. 1 near an end thereof, along the line 17-17 ofFIG. 12, and with a further portion broken away to show detail thereof.

FIG. 18 is an exploded front elevational view of a third embodiment of adynamic fixation connecting member assembly according to the inventionincluding an outer coil-like member and an inner threaded core.

FIG. 19 is an enlarged front elevational view of the dynamic fixationconnecting member of FIG. 18, showing the threaded core fully insertedin the coil-like member.

FIG. 20 is an enlarged cross-sectional view taken along the line 20-20of FIG. 19.

FIG. 21 is an enlarged and partial cross-sectional view of a portion ofthe assembly shown in FIG. 20.

FIG. 22 is an enlarged, partial and exploded perspective view of asecond, alternative dynamic fixation bone screw assembly according tothe invention including a bone screw shank, a receiver, a retainingstructure, a first lower compression member, the dynamic fixationconnecting member assembly of FIG. 10, a second upper compression memberand a closure member.

FIG. 23 is an enlarged front elevational view of the closure member ofFIG. 22.

FIG. 24 is a cross-sectional view taken along the line 24-24 of FIG. 23.

FIG. 25 is an enlarged top plan view of the closure member of FIG. 23.

FIG. 26 is an enlarged perspective view of the upper compression memberof FIG. 22.

FIG. 27 is an enlarged front elevational view of the upper compressionmember of FIG. 26.

FIG. 28 is an enlarged side elevational view of the upper compressionmember of FIG. 26.

FIG. 29 is an enlarged and partial cross-sectional view of the closuremember, similar to FIG. 24 and further showing the upper compressionmember in front elevation prior to attachment to the closure member.

FIG. 30 is an enlarged and partial cross-sectional view of the closuremember and front elevational view of the upper compression member,similar to FIG. 29, showing the upper compression member attached to theclosure member and free to rotate with respect thereto.

FIG. 31 is an enlarged and partial front elevational view of theassembly of FIG. 22 with portions broken away to show the detail thereofand further showing the upper compression member and closure memberpartially inserted in the receiver.

FIG. 32 is an enlarged and partial front elevational view similar toFIG. 31 showing the upper compression member and closure member fullyseated in the receiver prior to removal of the closure member break-offhead.

FIG. 33 is an enlarged and partial front elevational view of theassembly of FIG. 22 with portions broken away to show the detailthereof, and further showing the closure member break-off head removed.

FIG. 34 is an enlarged and partial front elevational view, similar toFIG. 32, with portions broken away to show the detail thereof andfurther showing the longitudinal connecting member assembly and uppercompression structure of FIG. 32 being replaced by a solid rod and areplacement upper compression structure.

FIG. 35 is an exploded and partial front elevational view of a fourthembodiment of a dynamic fixation connecting member assembly according tothe invention including a coil-like member, a cylindrical core withfixed integral and adjustable supports having helically woundprojections.

FIG. 36 is a partial cross-sectional view taken along the line 36-36 ofFIG. 35.

FIG. 37 is a partial and exploded perspective view of a third embodimentof a dynamic fixation bone screw assembly according to the inventionincluding a bone screw shank, a receiver, a retaining structure, thedynamic fixation connecting member assembly of FIG. 35, and a closuremember.

FIG. 38 is an enlarged perspective view of an adjustable support of FIG.35.

FIG. 39 is a perspective view showing three bone screw assembliesaccording to FIG. 37 with the dynamic fixation connecting memberassembly of FIG. 35 and including two adjustable supports of FIG. 38,with a portion exploded and portions broken away to show detail thereof.

FIG. 40 is an exploded and partial front elevational view of a fifthembodiment of a dynamic fixation connecting member assembly according tothe invention including an outer coil-like member, an inner cylindricalcore and a solid rod integral to the cylindrical core.

FIG. 41 is an exploded and partial cross-sectional view taken along theline 41-41 of FIG. 40.

FIG. 42 is a cross-sectional view of the inner coil-like member, takenalong the line 42-42 of FIG. 40.

FIG. 43 is an exploded and partial front elevational view of a sixthembodiment of a dynamic fixation connecting member assembly according tothe invention including an outer coil-like member a threaded innercylindrical core and a solid rod integral with the threaded core.

FIG. 44 is an exploded and partial front elevational view of a seventhembodiment of a dynamic fixation connecting member assembly according tothe invention including an outer coil-like member, an inner cylindricalcore, at least one threaded insert and a solid rod integral with thecylindrical core.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure.

With reference to FIGS. 1-7, the reference numeral 1 generallydesignates a non-fusion dynamic stabilization longitudinal connectingmember assembly according to the present invention. The connectingmember assembly 1 includes an outer, cannulated coil-like connectingmember 4 and a solid cylindrical core or insert 8, receivable in thecoil-like member 4 and fixed thereto at only one end of the inert 8 aswill be described more fully below. The dynamic connecting memberassembly 1 cooperates with at least a pair of fixed or polyaxial bonescrew assemblies according to the invention, one of such assemblies,generally 10, being shown in the drawings. With reference to FIGS. 5-7,the assembly 10 includes a shank 14 that further includes a body 16integral with an upwardly extending, substantially cylindrical upper endor capture structure 18; a receiver or head 20; a retaining andarticulating structure 22; a first lower compression structure 24 and asecond upper compression structure 26. The shank 14, the receiver 20,the retaining and articulating structure 22 and the first compressionstructure 24 are preferably assembled prior to implantation of the shankbody 16 into a vertebra 28. It is noted that any reference to the wordstop, bottom, up and down, and the like, in this application refers tothe alignment shown in the various drawings, as well as the normalconnotations applied to such devices, and is not intended to restrictpositioning of the assemblies 1 and 10 in actual use.

FIGS. 5-7 further show a closure structure, generally 30, of theinvention for capturing the longitudinal connecting member assembly 1within the receiver 20. Upon installation, which will be described ingreater detail below, the closure structure 30 presses against thesecond compression structure 26 that in turn presses against the outercoil-like member 4 that in turn presses against the compressionstructure 24. The compression structure 24 in turn presses against theretaining and articulating structure 22 that is threadably mated or inother ways connected to the capture structure 18. As will be discussedin greater detail below, the compression structure 26 also pressesagainst the compression structure 24 and the compression structures 24and 26 bias the retaining and articulating structure 22 into fixedfrictional contact with the receiver 20, so as to substantially attachand orient the longitudinal connecting member assembly 1 relative to thevertebra 28 and yet allow for relative movement of the outer coil-likemember 4 with respect to the inner cylindrical core 8, providing relief(e.g., shock absorption) and protected movement with respect to flexion,extension, distraction and compressive forces placed on the assembly 1and two or more connected assemblies 10. The coil-like member 4 is alsoable to twist or turn with respect to the cylindrical core 8, providingrelief for torsional stresses. However, the solid inner core 8 does notparticipate in or provide any means for torsional elasticity or axialcompression and distraction along a length of the outer coil 4.

Furthermore, the receiver 20, the shank 14, the retaining andarticulating structure 22 and the compression structures 24 and 26cooperate in such a manner that the receiver 20 and the shank 14 can besecured at any of a plurality of angles, articulations or rotationalalignments relative to one another and within a selected range of anglesboth from side to side and from front to rear, to enable flexible orarticulated engagement of the receiver 20 with the shank 14 until bothare locked or fixed relative to each other. Alternatively, it isforeseen that the connecting assembly 1 could involve the use of anupper compression member in an open receiver that is integral or fixedin position with respect to a bone screw shank or bone hook, or that thereceiver could have limited angular movement with respect to the shank,such as a hinged connection.

The longitudinal connecting member assembly 1, best illustrated in FIGS.1-4 is elongate, with the outer coil-like member 4 being made from metalor metal alloys or other suitable materials, including plastic polymers,PEEK and UHMWP, and the inner cylindrical core 8 also made fromplastics, such as polyurethanes, or metals, preferably from a metal ormetal alloy that is coated or covered with a thin, hard slick materialapplied to it or chemically treated on it. Specifically, the core 8includes a solid elongate, smooth-surfaced cylinder 40 having a centralaxis A. It may at times include a stop or rim 42 integral or fixedlyattached to the cylinder 40 at an end 43 thereof. The stop 42 issubstantially coaxial with the cylinder 40. In the embodiment shown, thestop 42 includes a flat abutment surface 44 and an outer cylindricalsurface 46. A snap-on attachment nob or nub 48 protrudes in a radialdirection from a lower portion 49 of the elongate cylinder 40 and nearthe end 43 thereof. Near an opposite end 50 thereof, the cylinder 40does not include structure for fixed attachment to the coil-like member4. The cylinder 40 has a substantially uniform outer radius that isslightly smaller than an inner radius of an internal substantiallycylindrical surface 54 of the coil-like member 4, providing a slight gap51 about the cylinder 40 (FIG. 7), substantially annular incross-section, located between the cylinder 40 and the surface 54 whenthe cylinder 40 is inserted into and fully received by the coil-likemember 4. The gap 51 that spans along a substantial length of thecylinder 40 from the lower portion 49 to the end 50 allows for sliding,axial (back and forth) movement of the coil-like member 4 with respectto the cylinder 40, along the axis A as well as twisting or torsionalmovement by the member 4.

The coil-like member 4 is also substantially cylindrical with anexternal substantially cylindrical surface 52 and the internalsubstantially cylindrical and smooth surface 54 previously identifiedherein. The surface 54 defines a bore 56 with a circular cross section,the bore 56 extending completely or substantially through the coil-likemember 4. The member 4 has a substantially flat and annular end surface58 and a substantially flat and annular opposite end surface 59. Themember 4 further includes a helical slit 60 that extends therethroughfrom the external surface 52 to the internal surface 54 and beginning ata location 62 near the end surface 58 and winding along an entire orsubstantial length of the coil-like member 4. The slit 60 illustrated inFIG. 1 runs through the end surface 59 (shown in phantom).Alternatively, it is foreseen that the slit 60 may end at or near theend surface 59. It is also foreseen that the slit 60 may extend throughthe end surface 58. A circular, U-shaped surface 66 defines a recess 68at the internal surface 54 and located between the end surface 58 andthe location 62 marking the beginning of the helical slit 60. The recess68 is substantially annular and is sized and shaped to receive the nob48 at any location therealong when the inner core 8 is received in theouter coil-like member 4 with the surface 58 abutting the surface 44.The cooperation between the nob 48 and the recess 68 provides a “snap”fit between the core 8 and the outer coil-like member 4, fixing the core8 to the member 4 at the respective ends 43 and 58.

The coil-like member internal cylindrical surface 54 is of a slightlygreater diameter than an outer diameter of the cylinder 40, allowing foraxially directed sliding movement of the coil-like member 4 with respectto the solid cylinder 40. It is foreseen that the lower portion 49 ofthe cylinder 40 may have a diameter slightly greater than the diameterof a remainder of the solid cylinder 40, providing for frictionalengagement between the lower portion 49 and the internal surface 54 ofthe coil-like member 4, giving some additional attachment andreinforcement of the snap fit between the member 4 and the core 8 nearor at the nob 48. When the cylindrical core 8 is inserted in thecoil-like member 4 and the nob 48 engages the recess 68, the core 8extends completely or substantially through the bore 56 along the axis Aand along a substantial length of the coil-like member 4 to near the endsurface 59, with the end surface 50 being near or adjacent the endsurface 59. The coil-like member 4 is not fixed to the solid core 8 ator near the end surfaces 50 and 59. Furthermore, as will be describedmore fully below, the bone screw assembly 10 is sized and shaped tofrictionally engage the coil-like member 4 without crushing or otherwisefrictionally engaging or fixing the coil-like member 4 against the core8 within any cooperating bone screw assembly 10, thus allowing forrelative movement between the coil-like member 4 and the solid core 8along a substantial length of the assembly 1.

It is noted that the core 8 may be sized and made from such materials asto provide for a relatively more rigid assembly 1 or a relatively moreflexible assembly 1 with respect to flex or bendability along theassembly 1. Such flexibility therefore may be varied by changing theouter diameter of the core 8 and thus likewise changing the diametricsize of the coil-like member 4. Also, it is noted that longer assemblies1 may need to be stiffer and thus larger in diameter than shorterassemblies 1. In addition, since the distance between the bone screwassembly receivers or heads can vary, the coil-case assembly may need tobe more or less stiff.

It is foreseen that in order to keep scar tissue from growing into thecoil-like member 4 through the helical slit 60, an inner or outer sleeveor sheath-like structure may be placed, adhered or otherwise applied toeither the external surface 52 or the internal surface 54 of thecoil-like member 4. Such a sheath-like structure would be of a size andshape such that axial movement of the coil-like member 4 is not hinderedand thus any relative movement between the coil-like member 4 and thecylindrical core 8 is not hindered or prevented.

The shank 14 of the bone screw assembly 10, best illustrated in FIGS.5-7, is elongate, with the shank body 16 having a helically wound,radially outwardly extending bone implantable thread 122 axiallyextending from near a tip 124 of the body 16 to near a slanted or slopedsurface 126 that is adjacent to a smooth cylindrical surface 128 locatedadjacent to the capture structure 18. The laterally projectingcylindrical surface 128 includes a buttress stop feature for frictionalengagement with and placement of the retaining and articulatingstructure 22. During use, the body 16 utilizing the thread 122 forgripping and advancement is implanted into the vertebra 28 leading withthe tip 124 and driven down into the vertebra 28 with an installation ordriving tool so as to be implanted in the vertebra 28 to near the slopedsurface 126.

To provide a biologically active interface with the bone, an outersurface 129 of the shank body 16 that includes the thread 121 andextends between the surface 126 and the tip 124 is coated, perforated,made porous or otherwise treated 130. The treatment 130 may include, butis not limited to a plasma spray coating or other type of coating of ametal or, for example, a calcium phosphate; or

a roughening, perforation or indentation in the surface 129, such as bysputtering, sand blasting or acid etching, that allows for bony ingrowthor ongrowth. Certain metal coatings act as a scaffold for bone ingrowth.Bio-ceramic calcium phosphate coatings include, but are not limited to:alpha-tri-calcium phosphate and beta-tri-calcium phosphate (Ca₃(PO₄)₂,tetra-calcium phosphate (Ca₄P₂O₉), amorphous calcium phosphate andhydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, forexample, is desirable as hydroxyapatite is chemically similar to bonewith respect to mineral content and has been identified as beingbioactive and thus not only supportive of bone ingrowth, but activelytaking part in bone bonding.

The sloped surface 126 extends radially outward and axially upward fromthe shank body 16 to the cylindrical projection 128. Further extendingaxially from the projection 128 is the capture structure 18 thatprovides a connective or capture apparatus disposed at a distance fromthe threaded shank body 16 and thus at a distance from the vertebra 28when the body 16 is implanted in the vertebra 28.

The capture structure 18 is configured for connecting the shank 14 tothe receiver 20 and capturing the shank 14 in the receiver 20. Thecapture structure 18 has an outer substantially cylindrical surface 134having a helically wound guide and advancement structure thereon whichin the illustrated embodiment is a V-shaped thread 136 extending fromadjacent the cylindrical surface 128 to adjacent an annular top or uppersurface 138. The upper surface 138 is disposed substantiallyperpendicular to an axis of rotation B of the shank 14. A diameter ofthe cylindrical surface 134 measured between roots of the thread 136 issmaller than a diameter of the projected cylindrical surface 128. Adiameter measured between crests of the thread 136 is illustrated equalto and may be smaller than the diameter of the cylindrical surface 128.Although a simple thread 136 is shown in the drawings, it is foreseenthat other structures including other types of threads, such asbuttress, square and reverse angle threads, and non threads, such ashelically wound flanges with interlocking surfaces, may be alternativelyused in place of the thread 136 in alternative embodiments of thepresent invention.

A hex-shaped driving formation 144 extends from the upper surface 138into the capture structure 18. The driving formation 144 is sized andshaped to cooperate with a hex-driver for rotating and driving the shankbody 16 into bone. It is foreseen that other driving features orapertures, such as slotted, tri-wing, hexalobular (such as the 6-pointstar shaped pattern sold under the trademark TORX), spanner, or the likemay also be utilized according to the invention.

In the illustrated embodiment, the shank 14 is cannulated with a smallcentral bore 149 extending an entire length of the shank along axis B.The bore 149 is coaxial with the threaded body 16 and the capturestructure outer surface 134, providing a passage through the shankinterior for a length of wire or pin inserted into the vertebra 28 priorto the insertion of the shank body 16, the wire or pin providing a guidefor insertion of the shank body 16 into the vertebra 28.

Also with reference to FIGS. 5-7, the receiver 20 includes a base 150integral with a pair of opposed upstanding arms 152 that extend from thebase 150 to a top surface 154. The arms 152 form a U-shaped cradle anddefine a U-shaped channel 156 between the arms 152 and include an upperopening 157 and a lower seat 158 having substantially the same radius asthe outer coil-like member 4 of the longitudinal connecting memberassembly 1 for operably snugly receiving the member assembly 1.

Each of the arms 152 has an interior surface that defines an innercylindrical profile and includes a partial helically wound guide andadvancement structure 162. In the illustrated embodiment, the guide andadvancement structure 162 is a partial helically wound flangeformconfigured to mate under rotation with a similar structure on theclosure member 30, as described more fully below. However, it isforeseen that the guide and advancement structure 162 couldalternatively be a buttress thread, a square thread, a reverse anglethread or other thread like or non-thread like helically woundadvancement structures for operably guiding under rotation and advancingthe closure 30 downward between the arms 152 and having such a nature asto resist splaying of the arms 152 when the closure 30 is advanced intothe U-shaped channel 156.

Each of the arms 152 includes a V-shaped or undercut tool engagementgroove 164 formed on a substantially planar outer surface 166 thereofwhich may be used for holding the receiver 20 with a holding tool (notshown) having projections that are received within the grooves 164during implantation of the shank body 16 into the vertebra 28. Thegrooves 164 may also cooperate with a holding tool during bone screwassembly and during subsequent installation of the connecting member 1and closure 30. It is foreseen that tool receiving grooves or aperturesmay be configured in a variety of shapes and sizes and be disposed atother locations on the arms 152.

Communicating with the U-shaped channel 156 and located within the base150 of the receiver 20 is a chamber or cavity 178 partially defined byan inner cylindrical surface 180 and a substantially spherical seatingsurface 182, the cavity 178 opening upwardly into the U-shaped channel156. The base 150 further includes a restrictive neck 183 adjacent theseating surface 182. The neck 183 defines an opening or borecommunicating with the cavity 178 and a lower exterior 186 of the base150. The neck 183 is conically counterbored or beveled to widen theangular range of the shank 14. The neck 183 is sized and shaped to besmaller than a radial dimension of a fixed or fully expanded retainingand articulating structure 22 so as to form a restriction at thelocation of the neck 183 relative to the retaining and articulatingstructure 22, to prevent the structure 22 from passing from the cavity178 and out into the lower exterior 186 of the receiver 20 when theretaining and articulating structure 22 is seated on the seating surface182. It is foreseen that the retaining and articulating structure couldbe compressible (such as where such structure has a missing section) andcould be loaded through the neck 183 and then allowed to expand andfully seat in the spherical seating surface 182. Other bottom loadingcapture structures could be utilized.

The retaining and articulating structure 22 has an operational centralaxis that is the same as the elongate axis B associated with the shank14. The retaining and articulating structure 22 has a central bore 190that passes entirely through the structure 22 from a top surface 192 toa bottom surface 194 thereof. An inner cylindrical surface 196 defines asubstantial portion of the bore 190, the surface 196 having a helicallywound guide and advancement structure thereon as shown by a v-shapedhelical rib or thread 198 extending from adjacent the top surface 192 tonear the bottom surface 194. Although a simple helical rib 198 is shownin the drawings, it is foreseen that other helical structures includingother types of threads, such as buttress and reverse angle threads, andnon threads, such as helically wound flanges with interlocking surfaces,may be alternatively used in an alternative embodiment of the presentinvention. The inner cylindrical surface 196 with the thread 198 areconfigured to mate under rotation with the capture structure outersurface 134 and helical guide and advancement structure or thread 136.

The illustrated retaining and articulating structure 22 has a radiallyouter partially spherically shaped surface 204 sized and shaped to matewith the partial spherically shaped seating surface 182 of the receiverand having a radius approximately equal to the radius associated withthe surface 182. The retaining and articulating structure radius islarger than the radius of the neck 183 of the receiver 20. Although notrequired, it is foreseen that the outer partially spherically shapedsurface 204 may be a high friction surface such as a knurled surface orthe like.

It is also foreseen that the retaining and articulating structure outersurface may be elliptical or ellipsoid in shape rather than spheroid inshape. Such an elliptical surface would be sized and shaped to contactand seat within a substantially spherical seating surface, such as theseating surface 182. Such an ellipsoid structure may be attachable tothe shank upper portion by threads, a pin, compression, or the like aspreviously described with respect to the substantially sphericalretaining and articulating structure 22. Furthermore, it is foreseenthat an ellipsoid retaining structure may be integral with the bonescrew shank and may include threads that allow the ellipsoid to bethreadably received into a base of a bone screw receiver. Again, it isforeseen that other types of retaining structure, articulating and not,could be used to keep the upper end of the shank contained within thereceiver.

The illustrated retaining and articulating structure top surface 192extends from the central bore 190 to the outer surface 204. The topsurface 192 is disposed perpendicular to an axis of rotation of thestructure 22. The bottom surface 294 also is disposed perpendicular tothe structure 22 axis of rotation.

The lower compression structure 24 includes a body 210 of substantiallycircular cross-section integral with a pair of upstanding arms 212. Thebody 210 and arms 212 form a generally U-shaped, open, through-channel214 having a partially U-shaped bottom seating surface 216 having aradius substantially conforming to an outer radius of the coil-likemember 4 and thus configured to operably snugly engage the coil member 4at the outer surface 52 thereof. The arms 212 disposed on either side ofthe channel 214 each include a top surface 218 that is parallel to anannular bottom surface 220. The compression structure 24 includes asubstantially cylindrical outer surface 222 and an inner cylindricalwall 224 defining a central through-bore extending along a central axisof the compression structure 24. The top surface 218 and the bottomsurface 220 are substantially parallel. Extending between the innercylindrical wall 224 and the bottom surface 220 is a curved or sphericalsurface 226 sized and shaped to frictionally engage and mate with theouter spherical surface 204 of the retaining and articulating structure22. The cylindrical surface 222 has a diameter slightly smaller than adiameter between crests of the guide and advancement structure 162allowing for top loading of the compression structure 24. Thecylindrical surface 222 diameter and a height of the compressionstructure 24 measured from the top surface 218 to the bottom surface 220are sized such that the compression structure 24 is received within thecylindrical surface 180 of the receiver 20 below the guide andadvancement structure 162, but the bottom surface 220 is spaced from asurface 227 of the receiver base 150 regardless of the angular positionof the shank 14 with respect to the receiver 20.

The upper or second compression structure 26 includes a body 230 ofsubstantially circular cross-section integral with a pair of downwardlyextending arms 232. The body 230 and the arms 232 form a generallyU-shaped, open, through-channel having a substantially U-shaped seatingsurface 236 having a radius substantially conforming to the outer radiusof the coil-like member 4 and thus configured to operably snugly engagethe coil member 4 at the external surface 52 thereof opposite the firstor lower compression structure 24. The arms 232 each included a bottomsurface 238 that is parallel to a planar top surface 240. Thecompression structure 26 includes a substantially cylindrical outersurface 242. A pin 244 of substantially circular cross section isdisposed centrally on the top surface 240 and extends upwardlytherefrom, being sized and shaped to fit within a central aperture ofthe closure 30 to be discussed more fully below. The cylindrical surface242 has a diameter slightly smaller than a diameter between crests ofthe guide and advancement structure 162 allowing for top loading of thecompression structure 26. The second compression structure 26 is sizedand shaped to abut against both the compression structure 24 and thecoil-like member 4 when pressed upon by the closure 30, allowing forclamping of the coil-like member 4 between the insert 26 and the insert24 as well as additional compressive force being placed against thecompression structure 24 that in turn presses the retaining andarticulating structure 22 against the spherical seating surface 182 ofthe receiver 20, clamping the bone screw shank 14 into a fixed angularposition with respect to the receiver 20 as illustrated in FIG. 7.

With reference to FIGS. 5-7, the closure structure 30 can be any of avariety of different types of closure structures for use in conjunctionwith the present invention with suitable mating structure on theupstanding arms 152 of the receiver 20. The closure structure 30 isrotatable between the spaced arms 152, but could be a slide-in closurestructure. The illustrated structure closure structure 30 issubstantially cylindrical and includes an outer helically wound guideand advancement structure in the form of a flange form 250. Theillustrated guide and advancement structure 250 operably joins with theguide and advancement structure 162 disposed on the interior of the arms152. In the illustrated embodiment, the flange form 250 has a protrusion251 that projects rearwardly from a trailing surface thereof thateffectively locks the closure structure 30 to the structure 162 withinwhich it is set so as to prevent splaying of the arms 152 upon whichmating guide and advancement structure 162 is mounted. The guide andadvancement structure 250 utilized in accordance with the presentinvention may take other forms, including those described in Applicant'sU.S. Pat. No. 6,726,689, which is incorporated herein by reference. Itis also foreseen that according to the invention the guide andadvancement structure 250 could alternatively be a buttress thread, asquare thread, a reverse angle thread or other thread like or non-threadlike helically wound advancement structure for operably guiding underrotation and advancing the closure structure 30 downward between thearms 152 and having such a nature as to resist splaying of the arms 152when the closure structure 30 is advanced into the U-shaped channel 156.

The closure structure 30 includes a lower surface 256 having a centralrecess 258 formed thereon. The recess 258 is substantially cylindricalhaving a central axis operationally coaxial with the receiver 20 and thesecond compression structure 26. The lower surface 256 is planar. Thecentral recess 258 is sized and shaped to receive the pin 244 of thecompression structure 26, with the lower surface 256 frictionallyengaging the top planar surface 240 of the compression structure 26 whenfully mated therewith, as illustrated in FIG. 7.

The closure structure 30 has a top surface 260 with an internal drive inthe form of an aperture 262, illustrated as a star-shaped internaldrive, for example, sold under the trademark TORX. A driving tool (notshown) sized and shaped for engagement with the internal drive 262 isused for both rotatable engagement and, if needed, disengagement of theclosure 30 from the arms 152. Although a star-shaped internal drive 258is shown in the drawings, the tool engagement structure may take avariety of tool-engaging forms and may include but is not limited to ahex shape or more than one aperture of various shapes. It is alsoforeseen that the closure structure 30 may alternatively include abreak-off head designed to allow such a head to break from a base of theclosure at a preselected torque, for example, 70 to 140 inch pounds.Such a closure structure would also include a base having an internaldrive to be used for closure removal.

During installation, the lower surface 256 engages the upper compressionstructure 26 that in turn engages the outer coil-like member 4 of theconnecting assembly 1. The closure structure 30 is rotated, using a toolengaged with the inner drive 262 until a selected pressure is reached atwhich point the longitudinal connecting assembly 1 is urged toward, butnot completely to the lower seat 158 of the channel 156. In turn, thecoil-like member 4 braces against the lower compression structure 24.The pressure placed on the outer surface of the coil-like member 4 bythe closure structure 30 is sufficient to clamp the member 4 between theupper and lower compression structures 24 and 26, but not enough tocrush or press the coil-like member 4 into fixed engagement with thecylinder 40 of the core 8 because of the engagement of the lowersurfaces 238 of the compression structure 26 with the top surfaces 218of the compression structure 24. Engagement between the surfaces 238 and218 allow for additional torquing of the closure structure 30 to fix thebone screw shank 14 between the compression structure 24 and thereceiver seating surface 182, without crushing the coil-like member 4against the core 8. For example, about 50 to about 80 inch pounds ofpressure are required for fixing the connecting assembly 1 in placewithout crushing the coil-like member 4 against the core 8. However,about 80 to about 120 inch pounds pressure may be required for fixingthe bone screw shank 14 with respect to the receiver 20. The cooperationbetween the compression members 24 and 26 at the surfaces 218 and 238,respectively, and the cradling of the assembly 1 between the compressionmembers 24 and 26 due to cylindrical inner surfaces thereof, allow for atotal torquing of 80 to 120 inch pounds, with only 50 to 80 inch poundsof that force being placed on the coil-like member 4.

Prior to the polyaxial bone screw assembly 10 being implanted in thevertebra 28, the retaining and articulating structure 22 is typicallyfirst inserted or top-loaded, into the receiver U-shaped channel 156,and then into the cavity 178 to dispose the structure 22 adjacent theinner seating surface 182 of the receiver 20. The shank capturestructure 18 is preloaded, inserted or bottom-loaded into the receiver20 at the neck bore 183. The retaining and articulating structure 22,now disposed in the receiver 20 is coaxially aligned with the shankcapture structure 18 so that the helical v-shaped thread 136 rotatinglymates with the thread 198 of the retaining and articulating structure22. The shank 14 and/or the retaining and articulating structure 22 arerotated to fully mate the structures 136 and 198, fixing the capturestructure 18 to the retaining and articulating structure 22. At thistime the shank 14 is in slidable and rotatable engagement with respectto the receiver 20, while the retaining and articulating structure 22and the lower aperture or neck 183 of the receiver 20 cooperate tomaintain the shank body 16 in rotational relation with the receiver 20.The shank body 16 can be rotated through a substantial angular rotationrelative to the receiver 20, both from side to side and from front torear so as to substantially provide a universal or ball joint whereinthe angle of rotation is only restricted by engagement of the slopedsurface 126 of the shank body 16 with the neck 183 of the receiver 20.

In the embodiment shown, the compression structure 24 is then loadedinto the receiver 20 with the U-shaped seating surface 216 aligned withthe receiver 20 U-shaped channel 156. The compression structure 24 isinitially top or down-loaded into the receiver 20 until the arms 212 aredisposed adjacent to the surface 180 and the bottom spherical surface226 is in contact with the surface 204 of the retaining and articulatingstructure 22. To ready the assembly 10 for implantation into bone, theshank 14, the receiver 20 and the compression structure 24 central axesare aligned along axis B, providing access to the hex-shaped formation144 on the shank capture structure 18 through the central bore formed bythe inner cylindrical wall 224 of the compression structure 24.

The assembly 10 is then typically screwed into a bone, such as thevertebra 28, by rotation of the shank 14 using a driving tool (notshown) with an Allen type driving formation that operably drives androtates the shank 14 by engagement thereof with the shank at the drivingformation 144. It is foreseen that in other embodiments according to theinvention, the hex-shaped driving formation 144 may be replaced by othertypes of foot print type tool engaging formations or recesses. Throughthe driving formation aperture, the retaining structure and the shankmay also be crimped together so as to not come apart with rotation.

At least two and up to a plurality of bone screw assemblies 10 areimplanted into vertebrae for use with the longitudinal connecting memberassembly 1. Each vertebra 28 may be pre-drilled to minimize stressingthe bone. Furthermore, when a cannulated bone screw shank is utilized,each vertebra will have a guide wire or pin (not shown) inserted thereinthat is shaped for the bone screw cannula 149 of the bone screw shankand provides a guide for the placement and angle of the shank 14 withrespect to the vertebra 28. A further tap hole may be made and the shankbody 16 is then driven into the vertebra 28, by rotation of the drivingtool (not shown). It is foreseen that the screws and the longitudinalconnecting member can be inserted in a percutaneous or minimallyinvasive surgical manner.

With particular reference to FIGS. 1-4, the longitudinal connectingmember assembly 1 is assembled by inserting the cylinder 40 of the core8 into the bore 56 defined by the inner cylindrical surface 54 of thecoil-like member 4. The end 50 of the core 8 is placed into the open end58 of the coil-like member 4 and the member 4 is moved toward the stopor rim 42 until the nub 48 snaps into the recess 68, with the end 58preferably in frictional contact with the flat abutment surface 44.

The connecting member assembly 1 is eventually positioned in an open orpercutaneous manner within the U-shaped channels 156 of two or more bonescrew assemblies 10. The assembly 1 can be straight, pre-bent orcurvilinear. The second or upper compression structure 24 is then placedin each assembly 10 with the U-shaped seating surface 236 facing thecoil-like member 4. The closure structure 30 is then inserted into andadvanced between the arms 152. As the closure structure 30 is rotatedbetween the arms 152, the central recess or aperture 258 receives thepin 244 of the compression member 26, centering the member 26 withrespect to the receiver 20 and the connecting member assembly 1.Continued rotation of the closure structure 30 results in engagementbetween the surfaces 240 and 256, uniformly pressing the compressionmember 26 against the coil-like member 4 at the seating surface 236 ofthe compression member 26 and the outer substantially cylindrical, butdiscontinuous surface 52 of the coil-like member 4. The coil-like member4 in turn presses downwardly against the seating surface 216 of thelower compression structure 24, pressing the structure 24 downwardlyinto engagement with the retaining and articulating structure outersurface 204 to set the angle of articulation of the shank body 16 withrespect to the receiver 20. As previously described, the compressionstructure 26 also presses against the compression structure 24 at thesurface 218 as the closure structure is torqued 30, clamping the shankbody 16 into a fixed position with respect to the receiver 20. However,the cylindrical surfaces 216 and 236 of the compression structures 24and 26, respectively, cradle and protect the coil-like member 4 fromcrushing against the core 8. Thus, although torquing of the closurestructure 30 against the compression structure 26 clamps the coil-likemember 4 with enough force to keep the member 4 in a fixed position inthe receiver 20, the upper and lower compression structures 24 and 26provide for the gap 51 to exist between the cylinder 40 of the core 8and the coil-like member 4 such that relative movement between thecylinder 40 and the member 4 is possible, along substantially the entirelength of the cylinder 40 with the exception of the end portion 49 thatis attached to the member 4 with the snap-on nob 48 and cooperatingrecess 68 formed by the inner surface 66. As will be described morefully below, in some embodiments according to the invention it ispossible to insert the closure structure pre-attached to the uppercompression structure with the two parts snapped together.

If removal of the assembly 1 from any of the assemblies 10 is necessary,or if it is desired to release the assembly 1 at a particular location,disassembly is accomplished by using the driving tool (not shown) with astar-shaped driving formation on the closure structure 30 internal drive262 to rotate and remove the closure structure 39 from the receiver 20.Disassembly of the assembly 10 is accomplished in reverse order to theprocedure described previously herein for assembly.

The polyaxial bone screw assembly 10 according to the inventionadvantageously allows for the removal and replacement of thelongitudinal connecting member assembly 1 with another longitudinalconnecting member having a different overall or outer diameter,utilizing the same receiver 20 and the same lower compression structure24. For example, as illustrated in FIGS. 8 and 9, the flexiblelongitudinal member connecting assembly 1 having an outer diameter F maybe removed and replaced by a more rigid assembly, such as a solid rod280 having an outer diameter G that is smaller than the diameter F ofthe outer coil-like member 4. The rod 280 is inserted into the receiveropening 157 followed by a cooperating upper compression structure 286,and then the closure structure 30 is re-inserted and tightened withinthe receiver 20. The upper compression structure 286 is substantiallysimilar to the compression structure 26 with the exception that thestructure 286 is sized and shaped to include a mating surface 288 forclosely cooperating with and contacting an outer cylindrical surface 290of the longitudinal connecting member 280. For example, in theembodiment shown, the surface 288 has an inner radius of curvaturealmost identical to an outer radius of curvature of the surface 290. Thecompression structure 286 further includes an upper pin 292 identical orsubstantially similar to the pin 244 described previously with respectto the compression structure 26. The pin 292 is receivable in thecentral recess 258 of the closure structure 30, ensuring that when fullyassembled in the receiver 20, the compression structure 26 is properlycentered and in full contact with the rod 280, which in turn centers therod 280 with respect to the lower compression member 24 for optimumcontact between the rod 280 and the lower compression member 24. It isnot necessary that the lower compression member 24 be in contact withthe rod 280 along the entire surface 216 thereof for adequate captureand fixing of the solid rod 280 with respect to the receiver 20 and theshank 14.

With reference to FIGS. 10-13, the reference numeral 1A generallydesignates a second embodiment of a non-fusion dynamic stabilizationlongitudinal connecting member assembly according to the presentinvention. The connecting member assembly 1A includes an outer,cannulated coil-like connecting member 4A and a substantiallycylindrical core or insert 8A, having an outer helical thread 9A, thecore being threadably receivable in the coil-like member 4A and fixedthereto at only one end of the core 8A as will be described more fullybelow. The dynamic connecting member assembly 1A cooperates with atleast a pair of polyaxial bone screw assemblies according to theinvention, one of such assemblies, generally 10, shown in FIGS. 14-17and previously described herein with reference to FIGS. 5-9. The closurestructure 30 also shown in FIGS. 14-17 and previously described hereinwith respect to FIGS. 5-7, also cooperates with the connecting member 1Aand the bone screw assembly 10 in the manner previously described hereinwith respect to the connecting member 1. The bone screw assembly 10 andcooperating closure 30, and in particular, the compression structures 24and 26 bias the retaining and articulating structure 22 into fixedfrictional contact with the receiver 20, so as to substantially attachand orient the longitudinal connecting member assembly 1A relative tothe vertebra 28 and yet allow for some relative movement of the outercoil-like member 4A with respect to the inner cylindrical core 8A,providing relief (e.g., shock absorption) with respect to flexion,extension and compressive and distractive forces placed on the assembly1A and two or more connected assemblies 10. The coil-like member 4A isalso able to twist or turn with respect to the cylindrical core 8A,providing relief for torsional stresses. However, the inner core 8A doesnot participate in or provide any means for torsional elasticity oraxial compression and distraction along a length of the outer coil 4A.

The longitudinal connecting member assembly 1A, best illustrated inFIGS. 10-13 is elongate, with both the outer coil-like member 4A and theinner core 8A being made from metal, metal alloys, composites or othersuitable materials, including plastic polymers, such as ultra-highmolecular weight polyethylene (UHMWP) and/or polyetheretherketone(PEEK). Also, in order to result in adequate hardness and low or no weardebris, the member 4A surfaces and the core 8A surfaces may be coatedwith an ultra thin, ultra hard, ultra slick and ultra smooth coating,such as may be obtained from ion bonding techniques and/or other gas orchemical treatments.

The core 8A illustrated in the drawing figures is solid, elongatecylinder, having a central axis AA. It is foreseen that the core 8A mayalso be a hollow cylinder. The core 8A includes a smooth cylindricalsurface 40A. The core 8A may include a stop or rim 42A integral orfixedly attached to the core 8A at an end 43A thereof. The stop 42A issubstantially coaxial with the cylinder 40A. In the embodiment shown,the stop 42A includes a flat abutment surface 44A and an outercylindrical surface 46A. As will be described in more detail below, thestop 42A may be replaced by an elongate connecting member, such as asolid rod, allowing for more rigid support, and fusion, if desired,along a portion of the spine adjacent to the spine portion receivingdynamic stabilization by the connector 1A.

The helical thread 9A extends radially outwardly from the surface 40A ofthe inner core 8A and winds about the inner core 8 substantially along alength thereof. The illustrated thread 9A includes an end portion 47Ahaving a thickness and radially length greater than a remainder portion48A of the thread 9A. The end portion 47A is sized and shaped to have anaxial length along the axis AA that corresponds to a width of thereceiver 20 that receives and clamps the assembly 1A into engagementwith the assembly 10. The core 8A is sized and shaped to attach to thecoil-like member 4A at the cylinder end 43A, with the end portion 47A ofthe thread 9A frictionally engaging the coil-like member 4A as will bedescribed more fully below. Near an opposite end 50A thereof, the core8A does not include structure for fixed attachment to the coil-likemember 4A. The cylindrical surface 40A has a substantially uniform outerradius that is slightly smaller than an inner radius of an internalsubstantially cylindrical surface 54A of the coil-like member 4A,providing a slight gap 51A about the cylindrical surface 40A, annular incross-section, located between the cylindrical surface 40A and thesurface 54A when the inner core 8A is inserted and threaded into andfully received by the coil-like member 4A. The gap 51A that spans alongthe length of the cylinder 40A from near the end stop 42A to the end 50Aallows for limited sliding, axial (back and forth) movement of thecoil-like member 4A with respect to the core 8A, along the axis AA aswell as some twisting or torsional movement by the member 4A about thecore 8A.

The outer coil-like member 4A is also substantially cylindrical with anexternal substantially cylindrical surface 52A and the internalsubstantially cylindrical and smooth surface 54A previously identifiedherein. The surface 54A defines a bore 56A with a circular crosssection, the bore 56A extending completely or substantially through thecoil-like member 4A. The member 4A has a substantially flat and annularend surface 58A and a curved or bullet-nosed opposite end 59A. It isnoted that in some embodiments, the end surface 59A may also besubstantially flat and annular. The bullet-nosed end 59A allows for easein implanting the assembly 1A, particularly in minimally invasive orless invasive procedures, that may be percutaneous in nature. The member4A further includes a helical slit 60A that extends therethrough fromthe external surface 52A to the internal surface 54A and beginning at alocation 62A at the end surface 58A and winding along an entire orsubstantial length of the coil-like member 4A. In the illustratedembodiment 1A, the slit 60A runs to near the bullet nose end 59A. Theslit 60A extends through the end surface 58A to allow for threadablymating the thread 9A of the inner core 8A with the slit 60A. Thecooperation between the thickened end portion 47A of the thread 9A andthe surfaces defining the slit 60A provide a friction or press fitbetween the inner core 8A and the outer coil-like member 4A, fixing thecore 8A to the member 4A near the respective ends 43A and 58A, butallowing for an axial gap or space between the remainder portion 48A ofthe thread 9A and the surfaces defining the slit 60A. When the innercore 8A is fully assembled within the coil-like member 4A, an outersurface 70A of the thread portion 47A is flush with the outer coilsurface 52A. Thus, a bone screw assembly 10 receiving and fixing thedynamic fixation assembly 1A near the stop or rim 42A frictionallyengages both the outer surface 52A of the coil-like member 4A and theouter surface 70A of the thread 9A of the inner core 8A. In theillustrated embodiment, the coil-like member internal cylindricalsurface 54A is of a slightly greater diameter than an outer diameter ofthe cylindrical surface 40A, allowing for axially directed slidingmovement of the coil-like member 4A with respect to the solid cylinder40A along the thread portion 48A. It is foreseen that a portion of thecylindrical surface 40A near the end 43A may have a diameter slightlygreater than the diameter of a remainder of the cylindrical surface 40A,providing for frictional engagement between the surface 40A and theinternal surface 54A of the coil-like member 4A, giving some additionalattachment and reinforcement of the friction fit between the threadportion 47A and the member 4A near the end 43A. When the cylindricalinner core 8A is inserted in the coil-like member 4A and the threadportion 47A frictionally engages the coil-like member 4A at the slit60A, the core 8A extends completely or substantially through the bore56A along the axis AA and along a substantial length of the coil-likemember 4A to near the end surface 59A, with the end surface 50A beingnear or adjacent the end surface 59A. The coil-like member 4A is notfixed to the solid core 8A at or near the end surfaces 50A and 59A. Alsoan outer surface 72A of the portion 48A of the thread 9A is not flushwith the outer surface 52A of the coil-like member, but rather inset orpositioned radially inwardly of the surface 52A, such that when the bonescrew assembly 10 frictionally engages the surface 52A, the surface 72Ais spaced from the bone screw assembly 10. Furthermore, similar to whatwas previously described with respect to the connector 1, the bone screwassembly 10 is sized and shaped to frictionally engage the coil-likemember 4A without crushing or otherwise frictionally engaging or fixingthe coil-like member 4A against the core 8A within a cooperating bonescrew assembly 10 located along the coil-like member 4A receiving theportion 48A of the thread 9A, thus allowing for relative movementbetween the coil-like member 4A and the core 8A.

As shown in the drawing figures, and in particular reference to FIGS. 13and 16, the substantial portion 48A of the thread 9A of the inner core8A is sized and shaped such that the thread portion 48A is uniformlyspaced from the surfaces defining the helical slit 60A of the coil-likemember 4A. In particular, the substantially square thread 9A includes aleading surface 74A and a trailing surface 76A. The coil-like member hassurfaces 78A and 80A that form the helical slit 60A. All along thethread portion 48A, the thread surface 74A is spaced from the surfacecoil surface 78A and the thread surface 76A is spaced from the coilsurface 80A. This spacing, along with the gap 51A between the outercylindrical surface 40A of the thread 9A and the inner surface 54A ofthe coil-like member 4A, allows for axial and twisting movement of theinner core 8A with respect to the coil-like member 4A until an axialmovement or motion is sufficient to cause the surface 74A to abutagainst the surface 78A and/or the surface 76A to abut against thesurface 80A. It is foreseen that the square thread 48A could be V-shapedor some other shape.

For the desired spacial alignment of the thread 9A with respect to theslit 60A to occur, the pitch of the slit 60A is substantially the sameas the pitch of the thread 9A of the core 8A. Pitch is the distancemeasured parallel to the axis AA, between corresponding points onadjacent thread forms in the same axial plane and on the same side ofthe axis. The amount or degree of pitch of the thread 9A and the slit60A may be chosen based upon the rigidity or stiffness requirements forthe assembly 1A and shock absorption desired. For example, it is notedthat increasing the pitch (i.e., forming a more acute angle between theslant of the thread 9A and the slit 60A with respect to the axis AA andtherefore increasing the distance between corresponding points onadjacent thread forms in the same axial plane) results in a stifferassembly with respect to bending and axial displacements. Furthermore, abenefit of increasing pitch is a lessening of impact loading between thethread 9A and the surfaces of the member 4A defining the helical slit60A. Stated in another way, when there is relative movement between thecoil-like member 4A and the core 8A such that surfaces 74A and 76A ofthe thread portion 48A abut against or make momentary impact withsurfaces 78A and 80A defining the slit 60A, when the pitch is greater,the facing surfaces 74A and 78A and also the facing surfaces 76A and 80Aslide with respect to one another rather than coming to an abrupt impactas occurs when the pitch is not as great. Therefore, increasing thepitch dampens the jolts of an impact between the surfaces of the threadportion 48A and the surfaces of the member 4A that define the slit 60A,thus improving shock absorption.

It is noted that the inner core 8A may be sized and made from suchmaterials as to provide for a relatively more rigid assembly 1A or arelatively more flexible assembly 1A with respect to flex or bendabilityalong the assembly 1A. Such flexibility therefore may be varied bychanging the outer diameter of the inner core 8A and thus likewisechanging the diametric size of the coil-like member 4A. Also, it isnoted that longer assemblies 1A may need to be stiffer and thus largerin diameter than shorter assemblies 1A. In addition, since the distancebetween the bone screw assembly heads can vary, the coil-like assemblymay need to be more or less stiff.

It is foreseen that in order to keep scar tissue from growing into thecoil-like member 4A through the helical slit 60A, an inner or outersleeve or sheath-like structure may be placed, adhered or otherwiseapplied to either the external surface 52A or the internal surface 54Aof the coil-like member 4A. Such a sheath-like structure would be of asize and shape such that axial movement of the coil-like member 4A isnot hindered and thus any relative movement between the coil-like member4A and the cylindrical core 8 is not hindered or prevented.

The longitudinal connecting member assembly 1A cooperates with the bonescrew assembly 10 and the closure structure 30 in the same manner aspreviously described herein with respect to the longitudinal connectingmember assembly 1. With particular reference to FIGS. 10-13, thelongitudinal connecting member assembly 1A is first assembled byinserting the inner core 8A into the bore 56A defined by the innercylindrical surface 54A of the coil-like member 4A. The end 50A of theinner core 8A is placed into the open end 58A of the coil-like member 4Awith the thread 9A being received by the slit 60A at the location 62A.The core 8A is then rotated, advancing the thread portion 48A toward thenose 59A until the thread portion 47A engages the surfaces 78A and 80Athat form the slit 60A, with the surface 44A of the stop 42A abuttingagainst the end surface 58A of the coil-like member. As illustrated inFIG. 13, the thread portion 47A, having a thickness greater than theportion 48A, frictionally engages the surfaces 78A and 80A at respectivesurfaces 74A and 76A, fixing the core 8A to the coil-like member 4A nearthe stop 42A.

The connecting member assembly 1A is eventually positioned in an open orpercutaneous manner within the U-shaped channels 156 of two or more bonescrew assemblies 10. The second or upper compression structure 24 isthen placed in each assembly 10 with the U-shaped seating surface 236facing the coil-like member 4A. The closure structure 30 is theninserted into and advanced between the arms 152. It is noted that it isalso possible to insert the closure structure pre-attached to the uppercompression structure with the two parts snapped together. As theclosure structure 30 is rotated between the arms 152, the central recessor aperture 258 receives the pin 244 of the compression member 26,centering the member 26 with respect to the receiver 20 and theconnecting member assembly 1A. Continued rotation of the closurestructure 30 results in engagement between the surfaces 240 and 256,uniformly pressing the compression member 26 against the coil-likemember 4A at the seating surface 236 of the compression member 26 andthe outer substantially cylindrical, but discontinuous surface 52A ofthe coil-like member 4A. The coil-like member 4A in turn pressesdownwardly against the seating surface 216 of the lower compressionstructure 24, pressing the structure 24 downwardly into engagement withthe retaining and articulating structure outer surface 204 to set theangle of articulation of the shank body 16 with respect to the receiver20.

With particular reference to FIG. 16, the compression structure 26 alsopresses against the compression structure 24 at the surface 218 as theclosure structure is torqued 30, clamping the shank body 16 into a fixedposition with respect to the receiver 20. However, the cylindricalsurfaces 216 and 236 of the compression structures 24 and 26,respectively, cradle and protect the coil-like member 4A from crushingagainst the inner core 8A. Thus, although torquing of the closurestructure 30 against the compression structure 26 clamps the coil-likemember 4A with enough force to keep the member 4A in a fixed position inthe receiver 20, the compression structures 24 and 26 allow formaintaining the gap 51A between the cylindrical surface 40A of the core8A and the coil-like member 4A, and also keep the thread portion 48Aspaced from the surfaces 78A and 80A that form the slit 60A and theouter surface 72A of the thread portion 48A spaced from the compressionmembers, such that relative movement between the inner core 8A and themember 4A is possible, along a length of the core 8A having the threadportion 48A thereon.

With reference to FIG. 17, a second bone screw assembly 10′ isillustrated, attached to the assembly 1A near the end stop 42A at thelocation of the thicker thread portion 47A. The assembly 10′ includes ashank 14′, a receiver 20′, a retaining and articulating structure 22′, afirst compression structure 24′, a second compression structure 26′ anda closure structure 30′ the same or substantially similar to therespective shank 14, receiver 20, retaining and articulating structure22, first compression structure 24, second compression structure 26 andclosure structure 30 of the assembly 10, and all other correspondingstructure previously described herein with respect to the assembly 10.As illustrated in FIG. 17, the outer surface 70A of the thread portion47A is flush with the outer surface 52A of the coil-like member 4A.Therefore, the compression structures 24′ and 26′ engage both thesurfaces 52A and 70A when the closure structure 30′ engages the receiver20′ and the compression structure 26′, fixing both the coil-like member4A and the inner core 8A within the receiver 20′ of the assembly 10′.

If removal of the assembly 1A from any of the assemblies 10 or 10′ isnecessary, or if it is desired to release the assembly 1A at aparticular location, disassembly is accomplished by using the drivingtool (not shown) with a star-shaped driving formation on the closurestructure 30 internal drive 262 to rotate and remove the closurestructure 39 from the receiver 20. Disassembly of the assembly 10 or 10′is accomplished in reverse order to the procedure described previouslyherein for assembly.

With reference to FIGS. 18-21 an alternative embodiment of a dynamiclongitudinal connecting member assembly, generally 301 is illustrated.The connecting member assembly 301 includes an outer, cannulatedcoil-like connecting member 304 and a substantially cylindrical core orinsert 308, having an outer helical thread 309 extending radially froman outer cylindrical surface 340, the core 308 being threadablyreceivable in the coil-like member 304 and fixed thereto at only one endnear an end stop 342, the thread 309 sized and shaped to be received inspaced relation to a helical slit 360 of the coil-like member 304. Thedynamic connecting member assembly 301 cooperates with at least a pairof polyaxial bone screw assemblies according to the invention, such asthe assembly 10 previously described herein.

The connecting member assembly 301 is substantially similar to theassembly 1A with the exception that the thread 309 is substantiallyuniform in size and shape along an entire length thereof, having anouter surface 372 that is disposed radially inwardly of an outer surface352 of the coil-like member 304, similar to the surface 72A of thethread portion 48A of the assembly 1A. Near the end stop 342, the core308 includes a cylindrical portion 384 of greater diameter than theremaining cylindrical surface 340, the portion 384 sized and shaped toprovide a frictional press fit between the coil-like member 304 and thecore 308 at only the portion 384, when the core 308 is fully received inthe coil-like member 304. Thus, other than at the portion 384, the corecylindrical surface 340 and the thread 309 are in slidable engagementwith the coil-like member 304.

It is noted that assemblies 1A, 301 and 10 according to the inventionadvantageously allow for replacement of the assembly 1A or 301 withother connecting member assemblies (dynamic or rigid) having the same orreduced outer diameter. For example, if it is found that a patientrequires a connecting member with additional rigidity, the closurestructures 30 may be removed, followed by removal of the uppercompression structure 26, followed by removal of the assembly 1A or 301and then an assembly 1A or 301 may be implanted having a slit withgreater pitch but the same outer diameter. Such an assembly may be morerigid, but would be sized and shaped to properly engage both the lowercompression structure 24 and the upper compression structure 26 and becradled, with the outer coil being held rigidly in place thereby. If, itis desired to replace the assembly 1A or 301 with a rigid rod having anouter diameter that is smaller than the outer diameter of the assembly1A or 301, such a rod may be placed on the lower compression structure24. Then, an upper compression structure sized and shaped to cooperatewith both the rigid rod and the closure structure 30 can be utilized tohold the rigid rod properly centered in place within the receiver 20.The fact that such a rigid rod of reduced diameter would not be closelyheld by the lower compression structure 24 is not of concern because theupper compression structure in combination with the closure structure 30provides adequate centering support.

With reference to FIGS. 22-34, the reference numeral 401 generallydesignates an alternative polyaxial bone screw assembly according to theinvention for use with the dynamic stabilization longitudinal connectingmember assemblies 1, 1A and 301 previously described herein and theassemblies 1B, 1C, 1D and 1E described below. The bone screw assembly401 includes a shank 414 that further includes a body 416 integral withan upwardly extending, substantially cylindrical upper end or capturestructure 418; a receiver or head 420 having a central axis C; aretaining and articulating structure 422; a first lower compressionstructure 424 and a second upper compression structure 426. The shank414, the receiver 420, the retaining and articulating structure 422 andthe first compression structure 424 are preferably assembled prior toimplantation of the shank body 416 into a vertebra (not shown). Theshank 414, the receiver 420 and the retaining and articulating structure422 are identical or substantially similar to the shank 14, receiver 20and retaining and articulating structure 22 previously described hereinwith respect to the bone screw assembly 10 and such discussion isincorporated by reference herein with respect to the assembly 401. Thelower compression structure 424 and the upper compression structure 426are substantially similar to the respective lower compression structure24 and the upper compression structure 26 of the assembly 10, with theexception that they cooperate with one another in a slidable fashionrather than abut one another. In particular, the upper compressionstructure 426 is receivable in the lower compression structure 424, withthe compression structures cooperating independently with a nestedset-screw type closure structure, generally 430, in a manner that willbe described in greater detail below.

FIGS. 22-25 show the nested set-screw type closure structure 430 of theinvention for capturing the longitudinal connecting member assembliesaccording to the invention, such as the assembly 1A, within the receiver420. The closure structure 430 includes an outer fastener 432 and anuploaded set screw 434. The fastener 432 includes a base 436 integral orotherwise attached to a break-off head 438. The base 436 cooperates withthe receiver 420 to capture the longitudinal connecting member 1A (orany other longitudinal connecting member according to the invention)within the bone screw receiver 420. The break-off installation head 438includes an internal drive or aperture 440 sized and shaped forengagement with a tool (not shown) for installing the fastener 432 tothe bone screw receiver 420 and thereafter separating the break-off head438 from a respective base 436 when installation torque exceeds selectedlevels.

The base 436 of the fastener portion 432 is substantially cylindrical,having an axis of rotation D and an external surface 450 having a guideand advancement structure 452 disposed thereon. The guide andadvancement structure 452 is matingly attachable to a guide andadvancement structure 453 of the bone screw receiver 420. Thecooperating guide and advancement structures 452 and 453 can be of anytype, including V-type threads, buttress threads, reverse angle threads,or square threads, and are preferably helically wound flange forms thatinterlock and are splay resistant, and thus do not exert radiallyoutward forces on the arms of the receiver 420, thereby avoidingtendencies toward splaying of the receiver arms when the fastenerportion 432 is tightly torqued into the receiver 420.

The fastener portion 432 includes an internal, centrally located bore454. At the base 436 the bore 454 is substantially defined by a guideand advancement structure, shown in FIG. 24 as an internal V-shapedthread 456. The thread 456 is sized and shaped to receive the threadedset screw 434 therein as will be discussed in more detail below.Although a traditional V-shaped thread 456 is shown, it is foreseen thatother types of helical guide and advancement structures may be used.Near a top of the base 436, an abutment shoulder 460, extends uniformlyradially inwardly. The abutment shoulder 460 is spaced from the V-shapedthread 456 and sized and shaped to be a stop for the set screw 434,prohibiting the set screw 434 from advancing upwardly out of the base436. It is foreseen that alternatively, the set screw may be equippedwith an outwardly extending abutment feature near a base thereof, withcomplimentary alterations made in the fastener base 436, such that theset screw 434 would be prohibited from advancing upwardly out of the topof the base 436 due to abutment of such outwardly extending featureagainst a surface of the base 436.

An inner cylindrical wall 462 separates the abutment shoulder 460 fromthe thread 456. The cylindrical wall 462 has a diameter equal to orslightly greater than a root or major diameter of the internal thread456. The wall 462 partially defines a cylindrical space or passage 464for axial adjustable placement of the screw 434 with respect to thelongitudinal connecting member 1A.

The fastener break-off head 438 is integral or otherwise attached to thefastener 432 at a neck or weakened region 466. The neck 466 isdimensioned in thickness to control the torque at which the break-offhead 438 separates from the fastener 432. The preselected separationtorque of the neck 466 is designed to provide secure engagement betweenthe fastener 432 and the lower compression structure 424 that in turnpresses against the retaining and articulating structure 422 that isthreadably mated to the shank 414, clamping the shank 414 in a desiredangular orientation with respect to the receiver 420 and thelongitudinal connecting member 1A. The fastener 432 thus captures thelongitudinal connecting member 1A within the receiver 420 before thehead 438 separates, by abutting against the lower compression member 512without making contact with the coil-like member 4A. For example, 120inch pounds of force may be a selected break-off torque to lock the bonescrew shank in place without placing any pressure on the coil-likemember 4A. The illustrated internal driving feature 440 of the break-offhead 438 enables positive, non-slip engagement of the head 438 by aninstallation and torquing tool. Separation of the break-off head 438leaves only the more compact base 436 of the fastener 432 installed inthe bone screw receiver 420, so that the installed fastener 432 has alow profile. As will be described in greater detail below, the set screw434 may then be rotated and moved downwardly into secure engagement withthe coil-like member 4A without forcing the coil-like member intocontact with the threaded core 8A.

The base 436 of the fastener 432 preferably includes a ramped or inclinesurface or structure 468 for cooperating frictional engagement with aninclined surface 469 of the lower compression structure 424 as bestillustrated in FIGS. 31 and 32. Both surfaces 468 and 469 slopedownwardly radially from the guide and advancement structure 452 towardthe axes C and D when the fastener and compression structures areassembled in the receiver 420. Ramped contact between the fastener 432and the lower compression structure 424 strengthens the structure 424and prevents capture of the upper compression structure 426.

The uploadable set screw 434 has a substantially annular and planar top476 and a substantially annular and planar bottom 477. The screw 434 issubstantially cylindrical in shape and coaxial with the fastener 432.The screw 434 includes an outer cylindrical surface 478 disposed nearthe bottom 477 and a threaded surface 480 extending from the top 476 tothe cylindrical surface 478. The v-shaped thread 480 is sized and shapedto be received by and mated with the inner thread 456 of the fastenerbase 436 in a nested, coaxial relationship.

As illustrated, for example, in FIGS. 24 and 25, The set screw 434includes a central aperture 486 formed in the top 476 and defined byside walls 488 that define a driving feature similar to but of smallerdimensions than the driving feature 440 of the fastener 432. The drivingfeature further includes a seating surface or bottom 489, aiding in apositive, non-slip engagement by a set screw installment and removaltool (not shown) that may be inserted through the aperture formed by thedriving feature 440 of the fastener 432 and then into the aperture 486and into engagement with the walls 488 defining the set screw drivingfeature. A lower central aperture or bore 490 extends between thecentral aperture 486 and the bottom 477 of the set screw 434. The bore490 is sized and shaped to receive and hold an upper portion of theupper compression structure 426 as will be described more fully below.

With reference to FIG. 24, the central set screw aperture 486 cooperateswith the central internal bore 454 of the fastener 432 for accessing anduploading the set screw 434 into the fastener 432 prior to engagementwith the bone screw receiver 420. After the closure structure 430 isinserted and rotated in the bone screw receiver 420, and the break-offhead 438 is broken off, the set screw 434 is rotated by a tool engagingthe drive feature walls 488 to place the set screw bottom 477 intofrictional engagement with the outer coil-like member 4A. Suchfrictional engagement is therefore readily controllable by a surgeon sothat the coil-like member 4A remains in slidable engagement with thethread 9A of the core 8A. Furthermore, if desired, the set screw 434 maybe rotated to a further extent to result in pressure being placed on thethread 9A and/or the core 8A by the coil-like member 4A, resulting in afixed engagement between the set screw, coil and core.

There are circumstances under which it is desirable or necessary torelease the longitudinal connecting member 1A from the bone screwassembly 401. For example, it might be necessary for a surgeon tore-adjust components of a spinal fixation system, including thelongitudinal connecting member 1A, during an implant procedure,following an injury to a person with such a system implanted. In suchcircumstances, the tool that engages and rotates the set screw 434 atthe driving feature 488 may be used to remove both the set screw 434 andattached fastener base 436 as a single unit, with the set screw 434contacting and contained within the base 436 by the abutment shoulder460. Thus, rotation of the set screw tool engaged with the set screw 434backs both the set screw 434 and the fastener base 436 out of the guideand advancement structure 453 in the receiver 420, thereby releasing thelongitudinal connecting member 1A for removal from the bone screwreceiver 420 or repositioning of the longitudinal connecting member 1A.It is foreseen that other removal structures such as side slots or otherscrew receiving and engagement structures may be used to engage the setscrew 434 that is nested in the fastener base 436.

With reference to FIGS. 22, 31 and 32, the lower compression structure424 includes a substantially cylindrical body 510 integral with a pairof upstanding arms 512. The body 510 and arms 512 form a generallyU-shaped, open, through-channel 514 having a partially U-shaped bottomseating surface 516 having a radius substantially conforming to an outerradius of the coil-like member 4A and thus configured to operably snuglyengage the coil member 4A at the outer surface 52A thereof. The arms 512disposed on either side of the channel 514 each include a top flangedportion 518, each portion 518 including the ramped or inclined surface469 previously described herein, sized and shaped to engage the inclinedsurface 468 of the fastener 432. The compression structure 424 furtherincludes a bottom surface 520 and a substantially cylindrical outersurface 522. An inner cylindrical wall 524 defining a centralthrough-bore extends along a central axis of the compression structure424 and extends between the seating surface 516 and a substantiallyspherical surface 526. The surface 526 extends between the innercylindrical wall 524 and the bottom surface 520. The surface 526 issubstantially similar to the spherical surface 226 of the compressionstructure 24 previously described herein, the surface 526 being sizedand shaped to frictionally engage and mate with the outer sphericalsurface of the retaining and articulating structure 422. The cylindricalsurface 522 has an outer diameter slightly smaller than a diameterbetween crests of the guide and advancement structure 453 of thereceiver 420 allowing for top loading of the compression structure 424.The top surface portions 518 disposed on each of the upstanding arms 512may be snapped into place within the receiver 420 during installation asthe arms 512 have sufficient flexibility so that the flanged arms 512may be pressed toward one another during top loading, with the flangedtop portions 518 clearing the guide and advancement structure 453. Thelower compression structure 424 is sized such that the compressionstructure 424 is ultimately received within the cylindrical surface ofthe receiver 420 below the guide and advancement structure 453 with theflanged top portions 518 received in recesses formed below the guide andadvancement structure 453 and the bottom surface 520 being spaced fromthe receiver base. The receiver 420 fully receives the lower compressionstructure 424 and blocks the structure 424 from spreading or splaying inany direction. It is noted that assembly of the shank 414 and theretaining structure 422 within the receiver 420, followed by insertionof the lower compression structure 424 into the receiver 420 areassembly steps typically performed at the factory, advantageouslyproviding a surgeon with a polyaxial bone screw with the lower insertfirmly snapped into place and thus ready for insertion into a vertebra.The through-channel 514 is sized and shaped such that the uppercompression structure 426 is receivable in the channel 514 betweenopposed upper substantially planar walls 528 that define an upperportion of the channel 514 near the top surfaces 469, each wall 528extending upwardly to a respective inclined surface 469. Adequateclearance is provided such that the upper compression structure 426 isin slightly spaced or in sliding relationship with the walls 528,allowing for independent movement of the upper compression structure 426with respect to the lower compression structure 424 and thus intogreater or lesser frictional engagement with the coil-like member 4A bypressure being placed directly on the upper compression structure 426 bythe set screw 434.

With reference to FIGS. 26-30, the upper or second compression structure426 includes a body 530 having a pair of downwardly extending legs 532.The body 530 and the legs 532 form a generally U-shaped, open,through-channel having a substantially U-shaped seating surface 536having a radius substantially conforming to the outer radius of thecoil-like member 4A and thus configured to operably snugly engage thecoil member 4A at the external surface 52A thereof opposite the seatingsurface 516 of the lower compression structure 424. The legs 532 eachinclude a bottom surface 538 that is substantially parallel to a planartop surface 540. The compression structure 426 includes a pair ofopposed curved outer surfaces 542 substantially perpendicular to the topsurface 540 and extending between the top surface 540 and the seatingsurface 536. The curved surfaces 542 further extend along the legs 532and terminate at the bottom surfaces 538. A pair of opposedsubstantially planar outer surfaces 543 are disposed between the curvedsurfaces 542 and are also disposed substantially perpendicular to thetop surface 540, each planar surface 543 extending between the topsurface 540 and a respective bottom surface 538.

A pin 544 of substantially circular cross section is disposed centrallyon the top surface 540 and extends upwardly therefrom, being sized andshaped to fit within the centrally located lower bore 490 formed in theset screw 434. The pin 544 further includes a substantially cylindricalbase 546 and a U-shaped channel 548 formed by a pair of opposed, flangedarms 550 that extend from the base 546 upwardly and substantiallyparallel to one another. Each of the flanged arms includes a partiallyconical surface portion 551 and a flat bottom surface 552 that issubstantially parallel to the top planar surface 540 of the compressionstructure body 530. As illustrated in FIGS. 29 and 30, the pin 544 isreceivable in the bore 440 with surfaces forming the bore pressing anddeforming the flanged arms 550 toward one another as the uppercompression structure 426 is pressed against the set screw 434 that hasalready been up-loaded into a fastener portion 432. Once the conicalsurface portions 551 clear the bore 440 and enter the set screw aperture486, the flanged arms 550 return to the original upright andsubstantially parallel form with the surfaces 552 being in contact withand seated upon a portion of the bottom surface 489 as illustrated inFIG. 30. The flanged arms 550 thus keep the compression structure 426attached to the set screw 434 and yet rotatable with respect theretoabout an axis of rotation E of the cylindrical base 546 of the structurethat is coaxial with the axis D of the set screw 434 and fastener 432,providing a centered relationship between the closure structure 430 andthe compression structure 426 while allowing the compression structure426 to freely rotate into a position centered over and in grippingengagement with the longitudinal connecting member 1 when assembledthereon. Furthermore, if removal of the fastener and uploaded set screwis desired, the attached compression structure 426 is advantageouslyremoved along therewith.

With reference to FIGS. 24 and 29-33, in use, the set screw 434 isassembled with the fastener 432 by inserting a set screw tool (notshown) through the bore 454 of the fastener 432 and into the aperture486 of the set screw 434, with outer features of the tool engaging theinner walls 488 of the set screw 434. The set screw 434 is then uploadedinto the fastener 432 by rotation of the set screw 434 with respect tothe fastener 432 to mate the set screw thread 480 with the fastenerinner thread 456 until the set screw top surface 476 is spaced from theabutment shoulder 460, but substantially nested in the fastener 432,with only the cylindrical surface 478 extending from the fastener base436. The upper compression structure 424 is then attached to the setscrew 434 as previously described with the pin 544 being received by thebore 490 and inserted therethrough until the arms 550 are disposedwithin the aperture 486, with the lower surfaces 552 of the flanged armsseated on the bottom 489 of the set screw aperture 486, capturing theflanged arms 550 within the aperture 486. The nested assembly shown inFIG. 24 and attached to an upper compression structure as shown in FIGS.29 and 30 is now pre-assembled and ready for use with a bone screwreceiver 420 and cooperating longitudinal connecting member assembly 1A.

With reference to FIGS. 31 and 32, the longitudinal connecting member 1Ais eventually placed in the bone screw receiver 420 that has beenpreviously attached to the bone screw shank 414, retaining andarticulating structure 422 and lower compression structure 424. Adriving tool (not shown) is used to rotate the closure structure byengagement with the drive feature 440 of the break-off head 438, matingthe guide and advancement structures 452 and 453. During installation,the fastener inclined surface 468 frictionally engages the inclinedsurface 469 of the lower compression structure 424, that in turn pressesagainst the retaining and articulating structure 422 that is threadablymated to the capture structure at the shank upper end 418, biasing theretaining and articulating structure 422 into fixed frictional contactwith the receiver 420, such that the receiver 420 and the shank 414 canbe independently secured at a desired angle with respect to the receiverwhile the longitudinal connecting member 1A remains movable within thereceiver and yet substantially captured between the compressionstructures 424 and 426. With reference to FIG. 33, the closure structureis rotated until a selected pressure is reached at which time the head438 breaks off, preferably about 80 to about 120 inch pounds thatadequately fixes the bone screw shank 414 with respect to the receiver420. When the break-off head is removed, the upper compression structure426 is preferably in contact with the coil-like member 4A, but placinglittle if any pressure thereon. Then, a set screw driving tool (notshown) is inserted into the drive feature 488 and the set screw 434 isrotated downwardly, into contact with the coil-like member, pressing thecoil-like member 4A to a desired amount, preferably enough tosubstantially attach and orient the longitudinal connecting memberassembly 1A relative to the vertebrae and yet allow for some relativemovement of the outer coil-like member 4A with respect to the inner core8A, providing some relief (e.g., shock absorption) with respect toflexion, extension, compressive and distractive forces placed on theassembly 1A and two or more connected bone screw assemblies 401. Thecoil-like member 4A is also able to twist or turn with respect to thethreaded core 8A, providing relief for torsional stresses. However, thesolid core 8A does not participate in or provide any means for torsionalelasticity or axial compression and distraction along a length of theouter coil 4A. In most instances, the pressure placed on the outersurface of the coil-like member 4A by the set screw 434 is sufficient toclamp the member 4A between the upper and lower compression structures424 and 426, but not enough to crush or press the coil-like member 4Ainto fixed engagement with the inner core 8A. The cooperation betweenthe compression members 424 and 426 cradles the assembly 1A therebetweendue to the cylindrical inner surfaces thereof, with pressure from theindependent set screw 434 upon the upper compression member 426 ofpreferably approximately only 50 to about 80 inch pounds, that in turnplaces such pressure on the coil-like member 4A. However, if desired,the set screw 434 may be rotated further, placing additional pressure onthe coil-like member and further limiting or blocking relative movementbetween the core 8A and the coil-like member 4A.

The polyaxial bone screw assembly 401 according to the inventionadvantageously allows for the removal and replacement of thelongitudinal connecting member assembly 1A with another longitudinalconnecting member having a different overall or outer diameter,utilizing the same receiver 420 and the same lower compression structure424. For example, as illustrated in FIG. 34, the flexible longitudinalmember connecting assembly 1A is removed and replaced by a more rigidassembly, such as a solid rod 570 having an outer diameter that issmaller than an outer diameter of the coil-like member 4A. The rod 570is inserted into the receiver 420 followed by a cooperating uppercompression structure 572 attached to a replacement break-off headclosure structure 430′ identical to the closure structure 430. The uppercompression structure 572 is substantially similar to the compressionstructure 426 with the exception that the structure 572 is sized andshaped to include a mating surface 574 for closely cooperating with andcontacting an outer cylindrical surface of the replacement longitudinalconnecting member 570. It is not necessary that the lower compressionmember 424 be in full contact with the rod 570 for adequate capture andfixing of the solid rod 570 with respect to the receiver 420 and theshank 414 as the rod 570 is centered and received fully by thereplacement upper compression structure 572 that also includes a pin(not shown) that is centrally received in the set screw 434′ of thereplacement closure structure 430′.

With reference to FIGS. 35-39, the reference numeral 1B generallydesignates a non-fusion dynamic stabilization flexible longitudinalconnecting member assembly according to the present invention. Theconnecting member assembly 1B includes an outer, cannulated coil-likeconnecting member 4B and a solid cylindrical core 6B receivable in thecoil-like member 4B. The cylindrical core 6B generally includes at leastone integral support member 8B and one or more adjustable supportmembers 9B slidably mountable on the core 6B. Each support member 8B and9B includes an outer helically wound projection 12B and 13B,respectively, adapted for cooperation with the coil-like member 4B aswill be described more fully below.

The dynamic connecting member assembly 1B cooperates with at least apair of polyaxial bone screw assemblies according to the invention, onesuch assembly, generally 10B, is shown in FIG. 37 and three polyaxialbone screw assemblies 10B are shown in FIG. 39, cooperating with onedynamic connecting member assembly 1B. With reference to FIG. 37, theassembly 10B includes a shank 14B that further includes a body 16Bintegral with an upwardly extending, substantially cylindrical upper endor capture structure 18B; a receiver or head 20B; and a retaining andarticulating structure 22B. The shank 14B, the receiver 20B, and theretaining and articulating structure 22B are preferably assembled priorto implantation of the shank body 16B into a vertebra (not shown).

FIGS. 37 and 39 further show a closure structure 30B of the inventionfor capturing the longitudinal connecting member assembly 1B within thereceiver 20B. Upon installation, which will be described in greaterdetail below, the closure structure 30B presses against the outercoil-like member 4B and also the helical projection 12B or 13B of arespective support 8B or 9B that is disposed within the coil-like member4B. Therefore, the flexible coil-like member 4B is not crushed orotherwise deformed by the closure structure 30B. With respect to thesupport 9B, in addition to supporting the coil-like member 4B, thesupport 9B allows for relative movement between the core 6B and theportion of the coil-like member 4B supported by the support 9B. Thecoil-like member 4B supported by the support 8B or 9B in turn pressesagainst the shank upper portion 18B that is threadably mated to theretaining and articulating structure 22B.

As will be discussed in greater detail below, the retaining andarticulating structure 22B is in turn pressed into fixed frictionalcontact with the receiver 20B, so as to substantially attach and orientthe longitudinal connecting member assembly 1B relative to the vertebraand yet allow for relative movement of the coil-like member 4B withrespect to the inner cylindrical core 6B, providing relief (e.g., shockabsorption) with respect to tensile and compressive forces placed on theassembly 1B and two or more connected assemblies 10B. Also, because theadjustable supports 9B are slidably attached to the core 6B, thecoil-like member 4B may twist or turn with respect to the cylindricalcore 6B, providing relief for torsional stresses. The solid inner core6B, however, does not participate in or provide any means for torsionalelasticity or axial compression and distraction along a length of theouter coil-like member 4B. Furthermore, the receiver 20B, the shank 14B,and the retaining and articulating structure 22B cooperate in such amanner that the receiver 20B and the shank 14B can be secured at any ofa plurality of angles, articulations or rotational alignments relativeto one another and within a selected range of angles both from side toside and from front to rear, to enable flexible or articulatedengagement of the receiver 20B with the shank 14B until both are lockedor fixed relative to each other. Alternatively, it is foreseen that theconnecting assembly 1B may be inserted into a receiver for a hook orinto a receiver that is fixed in position with respect to a bone screwshank, such as a bone screw receiver with an integral shank extendingtherefrom, or within a receiver with limited angular movement withrespect to the shank, such as a hinged connection.

The longitudinal connecting member assembly 1B, illustrated in FIGS.35-38, is elongate, with the outer coil-like member 4B being made frommetal or metal alloy or other suitable materials, including plastics andcomposites; and the solid inner cylindrical core 6B, and the supports 8Band 9B also being made from metal, metal alloy, plastic or compositematerial. In order to reduce the production of micro wear debris, thatin turn may cause inflammation, it is possible to make the coil-likemember 4B from a different material than the core 6B. For example, thecoil-like member 4B may be made from a metallic material, such astitanium, while the core member 6B and attached support 8B may be madefrom polyethylene, such as an ultra high molecular weight polyethylene.Also, it may be desirable to coat the components with thin, hard,super-slick and super-smooth substances or otherwise design the support9B such that wear debris does not occur between the support 9B and thecore 6B. Such combinations result in lower friction between thecomponents 4B, 6B, 8B and 9B, and thus result in lower wear.Alternatively, the core may be made from metal and the coil-like membermade from some other material. Another alternative is to coat either thecoil-like member 4B or the core 6B with a material other than metal suchthat adjacent, sliding surfaces are not both metallic. Such metal tonon-metal cooperation desirably results in at most, minor amounts ofparticulate matter formed between cooperating surfaces of the coil-likemember 4B, the core 6B and the supports 8B and 9B.

With reference to FIGS. 35-39, the core 6B is solid and elongate, havinga central axis AB and a smooth cylindrical surface 40B. The support 8Bis integral or otherwise fixedly attached to the core 6B at thecylindrical surface 40B. In the illustrated embodiment of the assembly1B shown in FIGS. 35-39, that is designed for use with three bone screwassemblies 10B, the support 8B that is integral to the core 6B is at alocation 42B disposed substantially centrally between an end 44B and anopposite end 45B of the elongate core 6B. It is noted however, that theintegral or fixed support 8B may be at any location along the axis AB.For example, the integral support 8B is typically located near the end44B or the end 45B of the core (not shown) when only two bone screwassemblies 10B are used to hold a connecting assembly 1B. It may also bedesirable to have the fixed support 8B be near the end 44B or the end45B when a longer assembly 1B is implanted using three or more bonescrew assemblies. Thus the fixed or integral support 8B may be at anylocation along a length of the core 6B, providing support for thecoil-like member 4B at a particular bone screw assembly 10B, the surgeonthen readily adjusting the location of any other slidingly mountablesupport 9B based upon the location or locations of the other bone screwassemblies 10B being used to hold the connecting member assembly 1B inplace.

The helical projections 12B and 13B of the respective supports 8B and 9Bare sized and shaped to extend radially from the cylindrical surface 40Band wind about the surface 40B along the axis AB. An axially directedlength L of each helical form or projection 12B and 13B is sized to fitpartially or completely within the receiver 20B of the bone screwassembly 10B, providing stability to a portion of the coil-like member4B that is at least partially received within the receiver 20B andpressed upon by the closure structure 30B. The projections 12B and 13Bare sized and shaped to cooperate with the coil-like member 4B in sizeand helical pitch, extending radially into a helical slit of the member4B as will be described in greater detail below.

With respect to the support 9B, an inner cylindrical wall 48B defines athrough-bore 49B sized and shaped to receive the core 6B and slidinglymate with the outer cylindrical surface 40B thereof. The support 9B hasan outer cylindrical surface 52B from which the helical projection 13Bextends. The integral support 8B also includes an outer cylindricalsurface 54B from which the helical projection 12B extends. Thecylindrical surfaces 52B and 54 are both smooth and identical orsubstantially similar in outer radius and diameter. The radii of thecylindrical surfaces 52B and 54B are slightly smaller than an innerradius of an inner surface 55B of the coil-like member 4B, providing forsliding engagement between the surfaces 52B, 54B and the inner surface55B. Furthermore the cylindrical surface 40B of the core 6B has asubstantially uniform outer radius that is slightly smaller than theradii of the surfaces 52B and 54B, providing a gap of annularcross-section between the surface 40B and the inner surface 55B when thecore 6B is inserted in the coil-like member 4B and fully received in thecoil-like member 4B. Thus, with the exception of the one locationwherein the fixed support 8B engages the coil-like member 4B within abone screw assembly 10B, the core 6B can move relative to the coil-likemember 4B along the axis AB, including the portions of the core 6Bwithin bone screw assemblies 10B in which the coil-like member 4B issupported by a sliding, adjustable support 9B. Twisting or torsionalmovement of the coil-like member 4B is possible between bone screwassemblies 10B, with both the support 8B and the support or supports 9Bfixing the coil-like member 4B within a receiver 20B. However, becauseof the helically wound nature of the supports 8B and 9B, the coil-likemember 4B is not crushed by a closure structure 30B pressing thereon.

The coil-like member 4B is substantially cylindrical with an outersubstantially cylindrical surface 62B and the inner substantiallycylindrical and smooth surface 55B previously identified herein. Thesurface 55B defines a bore 66B with a circular cross section, the bore66B extending completely through the coil-like member 4B. The member 4Bhas an end surface 68B and an opposite end surface 69B. The member 43further includes a helical slit 72B that extends therethrough from theouter surface 62B to the inner surface 55B and beginning near the endsurface 68B and winding along an entire length of the coil-like member4B to near the end surface 69B. Alternatively, it is foreseen that theslit 72B may extend through one or both of the end surfaces 68B and 69B.A width measured across the slit 72B is only slightly larger than awidth of the helical projections 121B and 13B, such that when thecoil-like member 4B engages the supports 8B and 9B, the respectiveprojections 12B and 13B snugly fit with the member 43 by extending thereinto at the slit 72B, with respective end surfaces 76B and 77B of theprojections 12B and 13B being substantially flush with the outercylindrical surface 62B of the member 4B.

When the cylindrical core 6B is inserted in the coil-like member 4B themember 4B is rotated about the core 6B at the fixed support 8B until thecore 6B extends completely through the bore 66B along the axis AB andsubstantially along an entire length of the coil-like member 4B as shownin FIG. 36. Initially, the coil-like member 4B is only attached to thecore 6B by the projection 12B of the support 8B extending into the slit72B. The member 4B is not otherwise fixedly attached to the solid core6B. A support 9B may then be rotated about the core 6B with theprojection 13B being fed through the slit 72B until a desired locationof the support 9B is reached along the axis A corresponding to alocation of a bone screw assembly 10B relative to the bone screwassembly 10B cooperating with the coil-like member 4B at the support 8B.Any additional supports 9B (for supporting the member 4B at anyadditional bone screw assemblies 10B) are fed into the coil-like memberin the same manner until such supports 9B are at desired locations alongthe coil-like member 4B.

It is noted that the core 6B may be sized and/or made from suchmaterials so as to provide for a relatively rigid assembly or arelatively flexible assembly with respect to flex or bendability alongthe assembly 1B. Such flexibility therefore may be varied by changingthe outer diameter of the core 6B and thus likewise changing thediametric size of the coil-like member 4B or by changing the materialfrom which the core 6B and/or coil-like member 4B are made. Also, it isnoted that longer assemblies 1B may need to be stiffer and thus largerin diameter than shorter assemblies 1B. The flexibility of the assembly1B may also be varied by varying the pitch of the helical slit 72B.

It is foreseen that in order to keep scar tissue from growing into thecoil-like member 4B through the helical slit 72B, an inner or outersleeve or sheath-like structure may be placed, adhered or otherwiseapplied to either the outer surface 62B or the inner surface 55B of thecoil-like member 4B. Such a sheath-like structure would be of a size andshape such that axial movement of the coil-like member 4B is nothindered and thus any relative movement between the coil-like member 4Band the cylindrical core 6B is not hindered or prevented. Such asheath-like structure could also capture any wear debris.

The shank 14B of the bone screw assembly 10B, best illustrated in FIG.37, is elongate, with the shank body 16B having a helically wound boneimplantable thread 124B extending from near a neck 126B located adjacentto the capture structure 18B to a tip 128B of the body 16B and extendingradially outward therefrom. During use, the body 16B utilizing thethread 124B for gripping and advancement is implanted into a vertebraleading with the tip 128B and driven down into the vertebra with aninstallation or driving tool (not shown), so as to be implanted in thevertebra to near the neck 126B. The shank 14B has an elongate axis ofrotation generally identified by the reference letter BB.

To provide a biologically active interface with the bone, an outersurface 129B of the shank body 16B that includes the thread 124B andextends between the neck 126B and the tip 128B is coated, perforated,made porous or otherwise treated 130B. The treatment 130B may include,but is not limited to a plasma spray coating or other type of coating ofa metal or, for example, a calcium phosphate; or a roughening,perforation or indentation in the surface 129B, such as by sputtering,sand blasting or acid etching, that allows for bony ingrowth orongrowth. Certain metal coatings act as a scaffold for bone ingrowth.Bio-ceramic calcium phosphate coatings include, but are not limited to:alpha-tri-calcium phosphate and beta-tri-calcium phosphate (Ca₃(PO₄)₂,tetra-calcium phosphate (Ca₄P₂O₉), amorphous calcium phosphate andhydroxyapatite (Ca₁₀(PO₄)₆ (OH)₂). Coating with hydroxyapatite, forexample, is desirable as hydroxyapatite is chemically similar to bonewith respect to mineral content and has been identified as beingbioactive and thus not only supportive of bone ingrowth, but activelytaking part in bone bonding.

The neck 126B of the shank 14B extends axially outward and upward fromthe shank body 16B. The neck 126B is of reduced radius as compared to anadjacent top 132B of the body 16B. Further extending axially andoutwardly from the neck 126B is the capture structure 18B that providesa connective or capture apparatus disposed at a distance from the bodytop 132B and thus at a distance from the vertebra when the body 16B isimplanted in the vertebra. The capture structure 18B is configured forconnecting the shank 14B to the receiver 20B and capturing the shank 14Bin the receiver 20B. The capture structure 18B has an outersubstantially cylindrical surface having a helically wound guide andadvancement structure thereon which in the illustrated embodiment is aV-shaped thread 136B extending from near the neck 126B to adjacent to aseating surface 138B. Although a simple thread 136B is shown in thedrawings, it is foreseen that other structures including other types ofthreads, such as buttress, square and reverse angle threads, and nonthreads, such as helically wound flanges with interlocking surfaces, maybe alternatively used in alternative embodiments of the presentinvention.

The shank 14B further includes a tool engagement structure 140B disposednear a top end surface 142B thereof for engagement of a driving tool(not shown). The driving tool is configured to fit about the toolengagement structure 140B so as to form a socket and mating projectionfor both driving and rotating the shank body 16B into the vertebra.Specifically in the embodiment shown in FIG. 37, the tool engagementstructure 140B is in the shape of a hexagonally shaped extension headcoaxial with both the threaded shank body 16B and the threaded capturestructure 18B.

The top end surface 142B of the shank 14B is preferably curved ordome-shaped as shown in the drawings, for positive engagement with thelongitudinal connecting assembly 1B, when the bone screw assembly 10B isassembled, as shown in FIG. 39 and in any alignment of the shank 14Brelative to the receiver 20B. In certain embodiments, the surface 142Bis smooth. While not required in accordance with the practice of theinvention, the surface 142B may be scored or knurled to further increasefrictional engagement between the surface 142B and the assembly 1B.

The shank 14B shown in the drawings is cannulated, having a smallcentral bore 144B extending an entire length of the shank 14B along theaxis BB. The bore 144B is of circular cross-section and has a firstcircular opening 146B at the shank tip 128 and a second circular opening148B at the top surface 142B. The bore 144B is coaxial with the threadedbody 16B and the capture structure outer surface. Particularly useful inminimally and less invasive surgery, the bore 144B provides a passagethrough the shank 14B interior for a length of wire (not shown) insertedinto the vertebra prior to the insertion of the shank body 16B, the wireproviding a guide for insertion of the shank body 16B into the vertebra.

Also with reference to FIGS. 37 and 39, the receiver 20B includes a base150B integral with a pair of opposed upstanding arms 152B that extendfrom the base 150B to a top surface 154B. The arms 152B form a U-shapedcradle and define a U-shaped channel 156B between the arms 152B andinclude an upper opening 157B and a lower seat 158B having substantiallythe same radius as the outer coil-like member 4B of the longitudinalconnecting member assembly 1B for operably snugly receiving the memberassembly 1B.

Each of the arms 152B has an interior surface that defines an innercylindrical profile and includes a partial helically wound guide andadvancement structure 162B. In the illustrated embodiment, the guide andadvancement structure 162B is a partial helically wound flangeformconfigured to mate under rotation with a similar structure on theclosure member 30B, as described more fully below. However, it isforeseen that the guide and advancement structure 162B couldalternatively be a buttress thread, a square thread, a reverse anglethread or other thread like or non-thread like helically woundadvancement structures for operably guiding under rotation and advancingthe closure 30B downward between the arms 152B and having such a natureas to resist splaying of the arms 152B when the closure 30B is advancedinto the U-shaped channel 156B.

Each of the arms 152B includes a V-shaped-like undercut tool engagementgroove 164B formed on a substantially planar outer surface 166B thereofwhich may be used for holding the receiver 20B with a holding tool (notshown) having projections that are received within the grooves 164Bduring implantation of the shank body 16B into the vertebra. The grooves164B may also cooperate with a holding tool during bone screw assemblyand during subsequent installation of the connecting member 1B andclosure 30B. It is foreseen that tool attachment receiving grooves orapertures may be configured in a variety of sizes and shapes, includingradiused, and be disposed at other locations on the arms 152B.

Communicating with the U-shaped channel 156B and located within the base150B of the receiver 20B is a chamber or cavity 178B partially definedby an inner substantially spherical seating surface 182B, the cavity178B opening upwardly into the U-shaped channel 156B. The base 150Bfurther includes a restrictive neck 183B adjacent the seating surface182B. The neck 183B defines an opening or bore communicating with thecavity 178B and a lower exterior 186B of the base 150B. The neck 183B isconically counterbored or beveled to widen the angular range of theshank 14B. The neck 183B is sized and shaped to be smaller than a radialdimension of a fixed or fully expanded retaining and articulatingstructure 22B so as to form a restriction at the location of the neck183B relative to the retaining and articulating structure 22B, toprevent the structure 22B from passing from the cavity 178B and out intothe lower exterior 186B of the receiver 20B when the retaining andarticulating structure 22B is seated on the seating surface 182B. It isforeseen that the retaining and articulating structure could becompressible (such as where such structure has a missing section) andcould be up-loaded through the neck 183B and then allowed to expand andfully seat in the spherical seating surface 182B. It is further notedthat a retaining and articulating structure may or may not articulatewith respect to the receiver, but rather be in a collet or ring shapethat is fixed or stationary with respect to the receiver and articulateswith respect to the shank.

In the embodiment shown, the retaining and articulating structure 22Bhas an operational central axis that is the same as the elongate axis BBassociated with the shank 14B. The retaining and articulating structure22B has a central bore 190B that passes entirely through the structure22B from a top surface 192B to a bottom surface 194B thereof. An innercylindrical surface defines a substantial portion of the bore 190B andhas a helically wound guide and advancement structure thereon as shownby a v-shaped helical rib or thread 198B extending from adjacent the topsurface 192B to near the bottom surface 194B. Although a simple helicalrib 198B is shown in the drawings, it is foreseen that other helicalstructures including other types of threads, such as buttress, squareand reverse angle threads, and non threads, such as helically woundflanges with interlocking surfaces, may be alternatively used in analternative embodiment of the present invention. Also, non-helicalspline capture designs could be used. The inner thread 198B isconfigured to mate under rotation with the capture structure outersurface guide and advancement structure or thread 136B.

The illustrated retaining and articulating structure 22B has a radiallyouter partially spherically shaped surface 200B sized and shaped to matewith the partial spherically shaped seating surface 182B of the receiverand having a radius approximately equal to the radius associated withthe surface 182B. The retaining and articulating structure radius islarger than the radius of the neck 183B of the receiver 20B. Althoughnot required, it is foreseen that the outer partially spherically shapedsurface 200B may be a high friction surface such as a knurled surface, ashot-pinging surface, sand-blasted surface or the like.

With reference to FIGS. 37 and 39, the closure structure 30B can be anyof a variety of different types of closure structures for use inconjunction with the present invention with suitable mating structure onthe upstanding arms 152B of the receiver 20B. The closure structure 30Bis rotatable between the spaced arms 152B. It is foreseen the closurestructure could be slidingly side-loading. The illustrated structureclosure structure 30B is substantially cylindrical and includes an outerhelically wound guide and advancement structure in the form of a flangeform 250B. The illustrated guide and advancement structure 250B operablyjoins with the guide and advancement structure 162B disposed on theinterior of the arms 152B. The guide and advancement structure 250Butilized in accordance with the present invention may take the formsdescribed in Applicant's U.S. Pat. No. 6,726,689, which is incorporatedherein by reference. It is also foreseen that according to the inventionthe guide and advancement structure 250B could alternatively be abuttress thread, a square head, a reverse angle thread or other threadlike or non-thread-like helically wound advancement structure foroperably guiding under rotation and advancing the closure structure 30Bdownward between the arms 152B and having such a nature as to resistsplaying of the arms 152B when the closure structure 30B is advancedinto the U-shaped channel 156B. Again, the closure could be aside-loading wedge-like structure with a radiused bottom.

The closure structure 30B includes a lower substantially planar surface256B. The surface 256B frictionally engages both the coil-like member 4Band a surface 76B or 77B of a respective support 8B or 9B when rotatedbetween the arms 152B and fully mated with the receiver 20B. The closurestructure 30B has a top surface 260B having an internal drive in theform of an aperture 262B, illustrated as a hex-shaped inner drive. Adriving tool (not shown) sized and shaped for engagement with theinternal drive 262B is used for both rotatable engagement and, ifneeded, disengagement, of the closure 30B from the arms 152B. Although ahex-shaped internal drive 262B is shown in the drawings, the toolengagement structure may take a variety of tool-engaging forms and mayinclude but is not limited to a star-shaped internal drive, for example,sold under the trademark TORX, or more than one aperture of variousshapes. It is also foreseen that the closure structure 30B mayalternatively include a break-off head designed to allow such a head tobreak from a base of the closure at a preselected torque, for example,80 to 140 inch pounds. Such a closure structure would also include abase having an internal drive to be used for closure removal.

During installation, the lower surface 256B engages both the coil-likemember 4B and the projections 12B or 13B of a respective support 8B or9B of the connecting assembly 1B. The closure structure 30B is rotated,using a tool engaged with the inner drive 262B until a selected pressureis reached at which point the longitudinal connecting assembly 1B isurged toward, but not completely to the lower seat 158B of the channel156B. In turn, the coil-like member 4B and cooperating support 8B or 9Bpress directly against the upper surface 142B of the shank 14B. Thepressure placed on the assembly 1B by the closure structure 30B issufficient to clamp the member 4B between the structure 30B and theshank 14B, but the flexible coil-like member 4B is not crushed orotherwise deformed because of the support provided by the projection 12Bor 13B, with such projection directly resisting the clamping pressure asthe projection 12B or 13B is flush with an outer surface of thecoil-like member 4B.

In use, prior to the polyaxial bone screw assembly 10B being implantedin a vertebra, the retaining and articulating structure 22B is typicallyfirst inserted or top-loaded, into the receiver U-shaped channel 156B,and then into the cavity 178B to dispose the structure 22B adjacent theinner seating surface 182B of the receiver 20B. The shank capturestructure 18B is preloaded, inserted or bottom-loaded into the receiver20B at the neck bore 183B. The retaining and articulating structure 22B,now disposed in the receiver 20B is coaxially aligned with the shankcapture structure 18B so that the helical v-shaped thread 136Brotatingly mates with the thread 198B of the retaining and articulatingstructure 22B. The shank 14B and/or the retaining and articulatingstructure 22B are rotated to fully mate the structures 136B and 198B,fixing the capture structure 18B to the retaining and articulatingstructure 22B. At this time the shank 14B is in slidable and rotatableengagement with respect to the receiver 20B, while the retaining andarticulating structure 22B and the lower aperture or neck 183B of thereceiver 20B cooperate to maintain the shank body 16B in rotationalrelation with the receiver 20B. The shank body 16B can be rotatedthrough a substantial angular rotation relative to the receiver 20B,both from side to side and from front to rear so as to substantiallyprovide a universal or ball joint wherein the angle of rotation is onlyrestricted by engagement of the neck 126B of the shank body 16B with theneck 183B of the receiver 20B.

The assembly 10B is then typically screwed into a vertebra by rotationof the shank 14B using a driving tool (not shown) with a socket thatoperably drives and rotates the shank 14B by engagement thereof with theshank at the tool engagement structure 140B. It is foreseen that inother embodiments according to the invention, the hex-shaped drivingformation 140B may be replaced by other types of outer or inner toolengaging formations or recesses. The retaining structure and the shankmay also be crimped together so as to not come apart with rotation or aone-way unlocking thread form could be used.

At least two and up to a plurality of bone screw assemblies 10B areimplanted into vertebrae for use with the longitudinal connecting memberassembly 1B. Each vertebra may be pre-drilled to minimize stressing thebone. Furthermore, when minimally invasive surgical techniques arefollowed and a cannulated bone screw shank is utilized, each vertebrawill have a guide wire or pin (not shown) inserted therein that isshaped for the bone screw cannula 144B of the bone screw shank andprovides a guide for the placement and angle of the shank 14B withrespect to the vertebra. A further tap hole may be made and the shankbody 16B is then driven into the vertebra by rotation of the drivingtool (not shown).

With particular reference to FIG. 37, the longitudinal connecting memberassembly 1B is assembled by inserting the core 6B into the bore 66Bdefined by the inner cylindrical surface 55B of the coil-like member 4B.The end 44B of the core 6B is placed into the open end 69B of thecoil-like member 4B and the member 4B is moved in an axial direction ABtoward the fixed support 8B. When the support 8B abuts the end 69B, thecoil-like member 4B is rotated with respect to the core 6B, with theprojection 12B extending into the slit 72B and the coil-like member 4Bwinding about the projection 12B. Rotation of the coil-like member 4Bwith respect to the core 6B is continued until the fixed support 8B isat a desired location and the core 6B is substantially received withinthe coil-like member 4B along an entire length thereof. The location 42Bof the support 8B along the core 6B corresponds to a location of a bonescrew assembly 10B that has been implanted. An adjustable support 9B isthen inserted onto the core 6B at either end 44B or 45B, depending uponthe relative location of a second bone screw assembly 10B that has beenimplanted. The adjustable support 9B slidingly mounts on the core 6B andis then rotated such that the projection 13B is guided into the slit 72Band wound therethrough, with the outer surface 77B flush with the outersurface 62B of the coil-like member 4B. The support 9B is rotated untilthe support is at a distance from the support 8B that corresponds to adistance between two implanted bone screw assemblies 10B. If theassembly 1B is to be connected to more than two bone screw assemblies10B, additional supports 9B are mounted on the core 6B and rotatedwithin the coil-like member 4B in similar fashion. A tool (not shown)sized and shaped to engage the support 9B within the bore 66B isutilized to rotate the supports 9B.

The connecting member assembly 1B is eventually positioned within theU-shaped channels 156B of two or more bone screw assemblies 10B with thesupports 8B and 9B located within the receivers 20B. The closurestructure 30B is then inserted into and advanced between the arms 152B.As the closure structure 30B is rotated between the arms 152B, thesurface 256B makes contact with the coil-like member 4B outer surface62B and either the outer surface 76B of the projection 12B or the outersurface 77B of the projection 13B uniformly pressing the assembly 1Bagainst the shank top surface 142B, pressing the retaining andarticulating structure outer surface 200B against the seating surface182B to set the angle of articulation of the shank body 16B with respectto the receiver 20B. However, the supports 8B and 9B protect thecoil-like member 4B from being deformed and thus, at the support 9B, thecore 6B remains in sliding engagement with the support 9B.

If removal of the assembly 1B from any of the assemblies 10B isnecessary, or if it is desired to release the assembly 1B at aparticular location, disassembly is accomplished by using the closuredriving tool (not shown) on the closure structure internal drive 262B torotate and remove the closure structure 30B from the receiver 20B.Disassembly of the assembly 10B is accomplished in reverse order to theprocedure described previously herein for assembly. It is foreseen thatthe assembly could use fixed integral bone anchors, such as screws andhooks.

With reference to FIGS. 40-42, a fifth embodiment of a dynamiclongitudinal connecting member assembly according to the invention,generally 1C, is substantially identical to the assembly 1 illustratedin FIGS. 1-4, with the exception that the stop 42 is replaced by aconnecting member having a solid outer surface illustrated by a rod 42C.In particular, the assembly 1C includes an outer coil-like member 4C andan inner solid cylindrical core 8C identical or substantially similar tothe respective coil-like member 4 and the inner core 8 of the connectingmember assembly 1 previously described herein. Therefore details of thecoil-like member 4C and the inner core 8C will not be repeated here.

The inner core 8C is fixed or integral with a longitudinal connectingmember extension or solid rod 42C. The rod 42C is integral or fixedlyattached to the inner core 8C at a first end 43C thereof. The rod 42C issubstantially coaxial with the inner core 8C and may be of any desiredlength, measured from the end 43C to an opposite end 44C, for attachingto one or more bone screw assemblies. The illustrated rod 42C is solid,but it is foreseen that it may be hollow. The rod 42C has a circularcross section, but may also be of other shapes including rectangular,square, and other polygonal and curved cross-sections. In the embodimentshown, the rod 42C includes a flat abutment surface 45C and an outercylindrical surface 46C. In the illustrated embodiment, the cylindricalsurface 46C has an outer diameter that is approximately the same as anouter diameter of the coil-like member 4C allowing for attachment of thesame size polyaxial bone screw assembly 10 or 401. However, in certainembodiments, it may be desirable to have a more flexible rod 42C thatmay be of smaller diameter than the diameter of the coil-like member 4C,or in other instances, a slightly larger diameter, stiffer rod, eachrequiring a different sized bone screw receiver or receiver components.It is noted that a variety of hook and bone screw assemblies maycooperate with the solid rod surface 46C, including, but not limited tothe polyaxial bone screw assembly 10B described herein and also the bonescrew assembly described in detail in U.S. Pat. No. 6,716,214,incorporated by reference herein. The rod 42C is preferably of a lengthfor secure attachment to at least one bone screw with at least one othercooperating bone screw assembly 10 or 401 being attached to thelongitudinal connecting member at the coil-like member 4C, similar towhat is illustrated and described herein with respect to the coil-likemember 4 and shown in FIGS. 5-7 and 14-15. If a patient requires morerigid support along a substantial portion of the spine, the rod 42C maybe of a longer length to cooperate and attach with two or more bonescrews, each implanted on separate vertebra. Thus, an assembly 1Caccording to the invention may be used to provide protected movement ofthe spine along the coil-like member 4C and spinal fusion along thelength of the rod 42C. It is foreseen that the rods 42C and 8C could becurvilinear in use.

Near the end 43C, the inner core 8C includes a cylindrical portion 48Cof greater diameter than the remaining cylindrical surface of the core8C, the portion 48C sized and shaped to provide a frictional press fitbetween the coil-like member 4C and the inner core 8C at only theportion 48C, when the inner core 8C is fully received in the coil-likemember 4C. Thus, other than at the portion 48C, the coil-like member 4Cis movable or slidable along the inner core 8C. Other structure may beused to attach the coil-like member 4C to the inner core 8C at only onelocation, such as the snap-on nob 48 and cooperating recess 68 of theassembly 1 previously described herein.

With reference to FIG. 43, a sixth embodiment of a dynamic longitudinalconnecting member assembly according to the invention, generally 1D, issubstantially identical to the assembly 1A illustrated in FIGS. 10-13,with the exception that the stop 42A has been replaced by a solidconnecting member or rod 42D. In particular, the assembly 1D includes anouter coil-like member 4D and an inner solid cylindrical core 8D havinga helical thread 9D identical or substantially similar to the respectivecoil-like member 4A, the inner core 8A and the thread 9A of theconnecting member assembly 1A previously described herein. Thereforedetails of the coil-like member 4D and the inner threaded core 8D willnot be repeated here. Again, the connecting members could becurvilinear.

The inner core 8D is fixed or integral with a longitudinal connectingmember extension illustrated as a solid rod 42D. The rod 42D is attachedto the inner core 8D at a first end 43D thereof. In the embodimentshown, the rod 42D is substantially coaxial with the inner core 8D andmay be of any desired length, measured from the end 43D to an oppositeend 44D, for attaching to one or more bone screw assemblies. Theillustrated rod 42D is solid, but it is foreseen that it may be hollow.The rod 42D has a circular cross section, but may also be of othershapes including rectangular, square, and other polygonal and/or curvedcross-sections. In the embodiment shown, the rod 42D includes a flatabutment surface 45D and an outer cylindrical surface 46D. In theillustrated embodiment, the cylindrical surface 46D has an outerdiameter that is approximately the same as an outer diameter of thecoil-like member 4D allowing for attachment of the same size polyaxialbone screw assembly 10 or 401. However, in certain embodiments, it maybe desirable to have a more flexible rod 42D that may be of smallerdiameter than the diameter of the coil-like member 4D, or in otherinstances, a slightly larger diameter, stiffer rod, each requiring adifferent sized bone screw receiver or receiver components. It is notedthat a variety of bone screw assemblies may cooperate with the solid rodsurface 46D, including, but not limited to the polyaxial bone screwassembly 10B described herein and also the bone screw assembly describedin detail in U.S. Pat. No. 6,716,214, incorporated by reference herein.The rod 42D is preferably of a length for secure attachment to at leastone bone screw with at least one other cooperating bone screw assembly10 or 401 being attached to the longitudinal connecting member at thecoil-like member 4D, similar to what is illustrated and described hereinwith respect to the coil-like member 4A and shown, for example, in FIGS.14-15 and 22. If a patient requires more rigid support along asubstantial portion of the spine, the rod 42D may be of a longer lengthto cooperate and attach with two or more bone screws, each implanted onseparate vertebra. Thus, an assembly 1D according to the invention maybe used to provide protected movement of the spine along the coil-likemember 4D and spinal fusion along the length of the rod 42D.

With reference to FIG. 44, a seventh embodiment of a dynamiclongitudinal connecting member assembly according to the invention,generally 1E, is substantially identical to the assembly 1B illustratedin FIGS. 35-36, with the exception that a solid connecting member or rod42E is integral or otherwise fixed to an inner cylindrical core 6E. Inparticular, the assembly 1E includes an outer coil-like member 4E, theinner core 6E, and at least one threaded insert 9E receivable on thecore 6E, identical or substantially similar to the respective coil-likemember 4B, the inner core 6B and the threaded inserts 9B of theconnecting member assembly 1B previously described herein. Thereforedetails of the coil-like member 4E, core 6E and insert 9E will not berepeated here. Although not shown in FIG. 44, the core 6B may alsoinclude one or more fixed threaded support similar or identical to thesupport 8B previously described herein with respect to the core 6B.

The inner core 6E is fixed or integral with a longitudinal connectingmember extension illustrated as a solid rod 42E near an end 43E thereof.The rod 42E is substantially coaxial with the inner core 6E and may beof any desired length, measured from the end 43E to an opposite end 44E,for attaching to one or more bone screw assemblies. The illustrated rod42E is identical or substantially similar to the rods 42C and 42Ddescribed previously herein with the respective assemblies 1C and 1D.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

1. In a medical implant assembly having at least two bone attachmentstructures cooperating with a longitudinal connecting member, theimprovement wherein the longitudinal connecting member comprises: a) aninner cylindrical core with an axis and a discrete attachment location;and b) an outer coil-like member attachable to the cylindrical core atthe attachment location, the cylindrical core receivable in thecoil-like member along a substantial length thereof, the outer coil-likemember being in sliding engagement with the cylindrical core in both adirection along the axis and torsionally when the core is fixed to thecoil-like member at the core attachment location and the outer coil-likemember is clamped to at least one of the bone attachment structures. 2.The improvement of claim 1 wherein the core attachment location is neara first end of the core and the outer coil-like member is attached tothe inner core near a second end of the outer coil-like member.
 3. Theimprovement of claim 2 wherein the second end is fixedly attached nearthe first end with at least one of a snap-on connection and a press fitconnection.
 4. The improvement of claim 1 wherein the longitudinalconnecting member is a first longitudinal connecting member and furthercomprising a second longitudinal connecting member fixed to the firstlongitudinal connecting member, the second longitudinal connectingmember extending along the axis and away from the coil-like member, thesecond longitudinal connecting member being receivable in at least oneof the bone attachment structures.
 5. The improvement of claim 4 whereinthe second longitudinal connecting member is a solid rod.
 6. Theimprovement of claim 4 wherein the second longitudinal connecting memberis sized and shaped to receive at least two bone attachment structures.7. The improvement of claim 4 wherein the second longitudinal connectingmember is integral with the cylindrical core.
 8. The improvement ofclaim 4 wherein the core attachment location is near an end of the coreand the second longitudinal connecting member is fixed to the core nearthe end.
 9. The improvement of claim 1 further comprising first andsecond compression members disposed in at least one of the boneattachment structures, each compression member having an inner surfacesized and shaped for frictional engagement with the outer coil-likemember, the first and second compression members cooperating to clamponly the outer coil-like member to the bone attachment structure, theouter coil-like member remaining slidable with respect to the innercore.
 10. The improvement of claim 9 wherein the first compressionmember is sized and shaped to abut against the second compression memberwhen in contact with the outer coil-like member.
 11. The improvement ofclaim 9 wherein the first compression member is sized and shaped toslidingly cooperate with the second compression member when in contactwith the outer coil-like member.
 12. The improvement of claim 11 whereinthe first compression member is a lower compression member and thesecond compression member is an upper compression member and furthercomprising a closure structure having an outer fastener and an inner setscrew, the outer fastener sized and shaped to exclusively press againstthe lower compression member and the set screw sized and shaped toexclusively press against the upper compression member.
 13. Theimprovement of claim 1 wherein the cylindrical core has a helicallywound thread thereon.
 14. The improvement of claim 13 wherein the threadis directly attached to the cylindrical core.
 15. The improvement ofclaim 13 wherein the thread is disposed on a hollow insert, the insertslidingly receivable on the cylindrical core.
 16. The improvement ofclaim 1 wherein the cylindrical core is solid.
 17. The improvement ofclaim 1 wherein the cylindrical core is metallic.
 18. The improvement ofclaim 1 wherein at least one of the bone attachment structures has anopen receiver for receiving the longitudinal connecting member and ashank, the shank having a surface altered by at least one of a) asurface roughening treatment; and b) a coating to provide a bioactiveinterface between the bone attachment structure and a vertebra.
 19. Theimprovement of claim 18 wherein the shank surface is plasma coated. 20.The improvement of claim 18 wherein the shank surface is coated withcalcium phosphate.
 21. The improvement of claim 20 wherein the calciumphosphate is selected from the group consisting of alpha-tri-calciumphosphate, beta-tri-calcium phosphate tetra-calcium phosphate, amorphouscalcium phosphate, hydroxyapatite and mixtures thereof.
 22. Theimprovement of claim 1 wherein the coil-like member is tubular and has ahelical slit.
 23. The improvement of claim 22 wherein the longitudinalconnecting member has a sheath sized and shaped to prevent bone ingrowthin the helical slit.
 24. In a medical implant assembly including atleast three bone attachment structures and a longitudinal connectingmember, the improvement comprising a) a first flexible longitudinalconnecting member portion having a longitudinal axis, an inner core andan outer coil-like member; and b) a second longitudinal connectingmember portion integral with the inner core and extending along the axisaway from the outer coil-like member.
 25. The improvement of claim 24wherein a) the cylindrical core has a first end; and b) the outercoil-like member has an internal substantially cylindrical surface, anexternal substantially cylindrical surface and a second end, the outermember attachable to the first end of the cylindrical core only near thesecond end, the outer member further defining a helical slit extendingthrough the internal surface and the external surface and extendingalong a substantial length of the outer member, the cylindrical corereceivable in the outer member adjacent to the internal surface andextending along a substantial length of the outer member, the outermember being in sliding engagement with the cylindrical core in adirection along the axis and torsionally when the first end is fixedrelative to the second end and the external surface is attached to atleast one of the bone attachment structures.
 26. The improvement ofclaim 24 wherein the second longitudinal connecting member is a solidrod.
 27. In a medical implant assembly including at least two boneattachment structures, the improvement comprising: a) a longitudinalconnecting member having i) a cylindrical core with an axis, a threadand a first end; and ii) an outer coil-like member having a second end,the outer coil-like member fixed to the cylindrical core only near thesecond end, the cylindrical core and the thread being receivable in thecoil-like member along a substantial length thereof with at least asubstantial portion of the thread being spaced from the coil-likemember, the coil-like member being in sliding engagement with the corein both a direction along the axis and torsionally when the first end isfixed with respect to the second end.
 28. The improvement of claim 27further comprising: a) first and second compression members disposed ineach of the bone attachment structures, each compression member havingan inner surface sized and shaped for frictional engagement with theouter coil-like member, the first and second compression memberscooperating to clamp only the outer coil-like member to the boneattachment structure with the cylindrical core and thread remainingslidable with respect to the outer coil-like member.
 29. The improvementof claim 27 wherein the first end is fixedly attached near the secondend by at least one of a press fit engagement between a portion of thecore and the coil-like member and a press fit between a portion of thethread and the coil-like member.
 30. In a medical implant assemblyincluding at least two bone attachment structures and a longitudinalconnecting member, the improvement wherein the connecting member furthercomprises: a) an elongate core; b) a first support structure attached infixed relation to the core, the support structure having a first helicalprojection; c) an elongate outer flexible member having an innerpassage, an outer surface and a helical slit, the slit extending along alength of the member and from the inner passage through the outersurface, the core receivable in the passage with the first helicalprojection being slidably receivable in the slit and extendibletherethrough; and d) at least one second support structure having asecond helical projection, the second support structure slidable withrespect to the core, the second helical projection slidably receivablein the slit and extendible therethrough.
 31. The improvement of claim 30wherein the core has an end and a mid-portion and the first supportstructure is located at the end.
 32. The improvement of claim 30 whereinthe core has an end and a mid-portion and the first support structure islocated at the mid-portion.
 33. The improvement of claim 30 wherein thecore is made from a first material and the flexible member is made froma second material.
 34. The improvement of claim 33 wherein the flexiblemember is substantially made from metal and the core is substantially aplastic.
 35. The improvement of claim 30 wherein each bone attachmentstructure has an open receiver for receiving the longitudinal connectingmember and a shank, the shank having a surface altered by at least oneof a) a surface roughening treatment; and b) a coating to provide abioactive interface between the bone attachment structure and avertebra.
 36. The improvement of claim 30 wherein each bone attachmentstructure has an open receiver for receiving the longitudinal connectingmember and a cannulated shank.